diff --git a/parity/cli/mod.rs b/parity/cli/mod.rs
index cc7e1d4ce..6168d9432 100644
--- a/parity/cli/mod.rs
+++ b/parity/cli/mod.rs
@@ -463,6 +463,10 @@ usage! {
 
 
 		["API and Console Options – HTTP JSON-RPC"]
+			FLAG flag_jsonrpc_allow_missing_blocks: (bool) = false, or |c: &Config| c.rpc.as_ref()?.allow_missing_blocks.clone(),
+			"--jsonrpc-allow-missing-blocks",
+			"RPC calls will return 'null' instead of an error if ancient block sync is still in progress and the block information requested could not be found",
+
 			FLAG flag_no_jsonrpc: (bool) = false, or |c: &Config| c.rpc.as_ref()?.disable.clone(),
 			"--no-jsonrpc",
 			"Disable the HTTP JSON-RPC API server.",
@@ -1230,6 +1234,7 @@ struct Rpc {
 	keep_alive: Option<bool>,
 	experimental_rpcs: Option<bool>,
 	poll_lifetime: Option<u32>,
+	allow_missing_blocks: Option<bool>,
 }
 
 #[derive(Default, Debug, PartialEq, Deserialize)]
@@ -1697,6 +1702,7 @@ mod tests {
 			arg_jsonrpc_threads: 4,
 			arg_jsonrpc_max_payload: None,
 			arg_poll_lifetime: 60u32,
+			flag_jsonrpc_allow_missing_blocks: false,
 
 			// WS
 			flag_no_ws: false,
@@ -1973,6 +1979,7 @@ mod tests {
 				keep_alive: None,
 				experimental_rpcs: None,
 				poll_lifetime: None,
+				allow_missing_blocks: None
 			}),
 			ipc: Some(Ipc {
 				disable: None,
diff --git a/parity/cli/tests/config.full.toml b/parity/cli/tests/config.full.toml
index 8bf97cac6..7d3184a77 100644
--- a/parity/cli/tests/config.full.toml
+++ b/parity/cli/tests/config.full.toml
@@ -64,6 +64,7 @@ interface = "local"
 cors = ["null"]
 apis = ["web3", "eth", "net", "parity", "traces", "rpc", "secretstore"]
 hosts = ["none"]
+allow_missing_blocks = false
 
 [websockets]
 disable = false
diff --git a/parity/configuration.rs b/parity/configuration.rs
index 6bc90ec56..93f207c15 100644
--- a/parity/configuration.rs
+++ b/parity/configuration.rs
@@ -370,6 +370,7 @@ impl Configuration {
 				miner_extras: self.miner_extras()?,
 				stratum: self.stratum_options()?,
 				update_policy: update_policy,
+				allow_missing_blocks: self.args.flag_jsonrpc_allow_missing_blocks,
 				mode: mode,
 				tracing: tracing,
 				fat_db: fat_db,
@@ -1390,6 +1391,7 @@ mod tests {
 		let args = vec!["parity"];
 		let conf = parse(&args);
 		let mut expected = RunCmd {
+			allow_missing_blocks: false,
 			cache_config: Default::default(),
 			dirs: Default::default(),
 			spec: Default::default(),
diff --git a/parity/rpc_apis.rs b/parity/rpc_apis.rs
index 8acbae7c3..660ec6628 100644
--- a/parity/rpc_apis.rs
+++ b/parity/rpc_apis.rs
@@ -21,24 +21,24 @@ use std::sync::{Arc, Weak};
 
 pub use parity_rpc::signer::SignerService;
 
-use ethcore_service::PrivateTxService;
 use ethcore::account_provider::AccountProvider;
 use ethcore::client::Client;
 use ethcore::miner::Miner;
 use ethcore::snapshot::SnapshotService;
 use ethcore_logger::RotatingLogger;
-use sync::{ManageNetwork, SyncProvider, LightSync};
+use ethcore_private_tx::Provider as PrivateTransactionManager;
+use ethcore_service::PrivateTxService;
 use hash_fetch::fetch::Client as FetchClient;
 use jsonrpc_core::{self as core, MetaIoHandler};
 use light::client::LightChainClient;
-use light::{TransactionQueue as LightTransactionQueue, Cache as LightDataCache};
+use light::{Cache as LightDataCache, TransactionQueue as LightTransactionQueue};
 use miner::external::ExternalMiner;
-use parity_runtime::Executor;
 use parity_rpc::dispatch::{FullDispatcher, LightDispatcher};
 use parity_rpc::informant::{ActivityNotifier, ClientNotifier};
-use parity_rpc::{Metadata, NetworkSettings, Host};
+use parity_rpc::{Host, Metadata, NetworkSettings};
+use parity_runtime::Executor;
 use parking_lot::{Mutex, RwLock};
-use ethcore_private_tx::Provider as PrivateTransactionManager;
+use sync::{LightSync, ManageNetwork, SyncProvider};
 use updater::Updater;
 
 #[derive(Debug, PartialEq, Clone, Eq, Hash)]
@@ -106,7 +106,7 @@ impl FromStr for Api {
 			"signer" => Ok(Signer),
 			"traces" => Ok(Traces),
 			"web3" => Ok(Web3),
-			api => Err(format!("Unknown api: {}", api))
+			api => Err(format!("Unknown api: {}", api)),
 		}
 	}
 }
@@ -149,20 +149,20 @@ impl FromStr for ApiSet {
 			match api {
 				"all" => {
 					apis.extend(ApiSet::All.list_apis());
-				},
+				}
 				"safe" => {
 					// Safe APIs are those that are safe even in UnsafeContext.
 					apis.extend(ApiSet::UnsafeContext.list_apis());
-				},
+				}
 				// Remove the API
 				api if api.starts_with("-") => {
 					let api = api[1..].parse()?;
 					apis.remove(&api);
-				},
+				}
 				api => {
 					let api = api.parse()?;
 					apis.insert(api);
-				},
+				}
 			}
 		}
 
@@ -205,11 +205,9 @@ pub trait Dependencies {
 	fn activity_notifier(&self) -> Self::Notifier;
 
 	/// Extend the given I/O handler with endpoints for each API.
-	fn extend_with_set<S>(
-		&self,
-		handler: &mut MetaIoHandler<Metadata, S>,
-		apis: &HashSet<Api>,
-	) where S: core::Middleware<Metadata>;
+	fn extend_with_set<S>(&self, handler: &mut MetaIoHandler<Metadata, S>, apis: &HashSet<Api>)
+	where
+		S: core::Middleware<Metadata>;
 }
 
 /// RPC dependencies for a full node.
@@ -235,6 +233,7 @@ pub struct FullDependencies {
 	pub whisper_rpc: Option<::whisper::RpcFactory>,
 	pub gas_price_percentile: usize,
 	pub poll_lifetime: u32,
+	pub allow_missing_blocks: bool,
 }
 
 impl FullDependencies {
@@ -243,24 +242,39 @@ impl FullDependencies {
 		handler: &mut MetaIoHandler<Metadata, S>,
 		apis: &HashSet<Api>,
 		for_generic_pubsub: bool,
-	) where S: core::Middleware<Metadata> {
+	) where
+		S: core::Middleware<Metadata>,
+	{
 		use parity_rpc::v1::*;
 
 		macro_rules! add_signing_methods {
-			($namespace:ident, $handler:expr, $deps:expr, $nonces:expr) => {
-				{
-					let deps = &$deps;
-					let dispatcher = FullDispatcher::new(deps.client.clone(), deps.miner.clone(), $nonces, deps.gas_price_percentile);
-					if deps.signer_service.is_enabled() {
-						$handler.extend_with($namespace::to_delegate(SigningQueueClient::new(&deps.signer_service, dispatcher, deps.executor.clone(), &deps.secret_store)))
-					} else {
-						$handler.extend_with($namespace::to_delegate(SigningUnsafeClient::new(&deps.secret_store, dispatcher)))
-					}
+			($namespace:ident, $handler:expr, $deps:expr, $nonces:expr) => {{
+				let deps = &$deps;
+				let dispatcher = FullDispatcher::new(
+					deps.client.clone(),
+					deps.miner.clone(),
+					$nonces,
+					deps.gas_price_percentile,
+				);
+				if deps.signer_service.is_enabled() {
+					$handler.extend_with($namespace::to_delegate(SigningQueueClient::new(
+						&deps.signer_service,
+						dispatcher,
+						deps.executor.clone(),
+						&deps.secret_store,
+					)))
+				} else {
+					$handler.extend_with($namespace::to_delegate(SigningUnsafeClient::new(
+						&deps.secret_store,
+						dispatcher,
+					)))
 				}
-			}
+			}};
 		}
 
-		let nonces = Arc::new(Mutex::new(dispatch::Reservations::new(self.executor.clone())));
+		let nonces = Arc::new(Mutex::new(dispatch::Reservations::new(
+			self.executor.clone(),
+		)));
 		let dispatcher = FullDispatcher::new(
 			self.client.clone(),
 			self.miner.clone(),
@@ -271,13 +285,13 @@ impl FullDependencies {
 			match *api {
 				Api::Debug => {
 					handler.extend_with(DebugClient::new(self.client.clone()).to_delegate());
-				},
+				}
 				Api::Web3 => {
 					handler.extend_with(Web3Client::new().to_delegate());
-				},
+				}
 				Api::Net => {
 					handler.extend_with(NetClient::new(&self.sync).to_delegate());
-				},
+				}
 				Api::Eth => {
 					let client = EthClient::new(
 						&self.client,
@@ -291,91 +305,119 @@ impl FullDependencies {
 							allow_pending_receipt_query: !self.geth_compatibility,
 							send_block_number_in_get_work: !self.geth_compatibility,
 							gas_price_percentile: self.gas_price_percentile,
+							allow_missing_blocks: self.allow_missing_blocks,
 							allow_experimental_rpcs: self.experimental_rpcs,
 						}
 					);
 					handler.extend_with(client.to_delegate());
 
 					if !for_generic_pubsub {
-						let filter_client = EthFilterClient::new(self.client.clone(), self.miner.clone(), self.poll_lifetime);
+						let filter_client = EthFilterClient::new(
+							self.client.clone(),
+							self.miner.clone(),
+							self.poll_lifetime,
+						);
 						handler.extend_with(filter_client.to_delegate());
 
 						add_signing_methods!(EthSigning, handler, self, nonces.clone());
 					}
-				},
+				}
 				Api::EthPubSub => {
 					if !for_generic_pubsub {
-						let client = EthPubSubClient::new(self.client.clone(), self.executor.clone());
+						let client =
+							EthPubSubClient::new(self.client.clone(), self.executor.clone());
 						let h = client.handler();
-						self.miner.add_transactions_listener(Box::new(move |hashes| if let Some(h) = h.upgrade() {
-							h.notify_new_transactions(hashes);
-						}));
+						self.miner
+							.add_transactions_listener(Box::new(move |hashes| {
+								if let Some(h) = h.upgrade() {
+									h.notify_new_transactions(hashes);
+								}
+							}));
 
 						if let Some(h) = client.handler().upgrade() {
 							self.client.add_notify(h);
 						}
 						handler.extend_with(client.to_delegate());
 					}
-				},
+				}
 				Api::Personal => {
-					handler.extend_with(PersonalClient::new(&self.secret_store, dispatcher.clone(), self.geth_compatibility, self.experimental_rpcs).to_delegate());
-				},
+					handler.extend_with(
+						PersonalClient::new(
+							&self.secret_store,
+							dispatcher.clone(),
+							self.geth_compatibility,
+							self.experimental_rpcs,
+						).to_delegate(),
+					);
+				}
 				Api::Signer => {
-					handler.extend_with(SignerClient::new(&self.secret_store, dispatcher.clone(), &self.signer_service, self.executor.clone()).to_delegate());
-				},
+					handler.extend_with(
+						SignerClient::new(
+							&self.secret_store,
+							dispatcher.clone(),
+							&self.signer_service,
+							self.executor.clone(),
+						).to_delegate(),
+					);
+				}
 				Api::Parity => {
 					let signer = match self.signer_service.is_enabled() {
 						true => Some(self.signer_service.clone()),
 						false => None,
 					};
-					handler.extend_with(ParityClient::new(
-						self.client.clone(),
-						self.miner.clone(),
-						self.sync.clone(),
-						self.updater.clone(),
-						self.net_service.clone(),
-						self.secret_store.clone(),
-						self.logger.clone(),
-						self.settings.clone(),
-						signer,
-						self.ws_address.clone(),
-						self.snapshot.clone().into(),
-					).to_delegate());
+					handler.extend_with(
+						ParityClient::new(
+							self.client.clone(),
+							self.miner.clone(),
+							self.sync.clone(),
+							self.updater.clone(),
+							self.net_service.clone(),
+							self.secret_store.clone(),
+							self.logger.clone(),
+							self.settings.clone(),
+							signer,
+							self.ws_address.clone(),
+							self.snapshot.clone().into(),
+						).to_delegate(),
+					);
 
 					if !for_generic_pubsub {
 						add_signing_methods!(ParitySigning, handler, self, nonces.clone());
 					}
-				},
+				}
 				Api::ParityPubSub => {
 					if !for_generic_pubsub {
 						let mut rpc = MetaIoHandler::default();
-						let apis = ApiSet::List(apis.clone()).retain(ApiSet::PubSub).list_apis();
+						let apis = ApiSet::List(apis.clone())
+							.retain(ApiSet::PubSub)
+							.list_apis();
 						self.extend_api(&mut rpc, &apis, true);
-						handler.extend_with(PubSubClient::new(rpc, self.executor.clone()).to_delegate());
+						handler.extend_with(
+							PubSubClient::new(rpc, self.executor.clone()).to_delegate(),
+						);
 					}
-				},
+				}
 				Api::ParityAccounts => {
-					handler.extend_with(ParityAccountsClient::new(&self.secret_store).to_delegate());
-				},
-				Api::ParitySet => {
-					handler.extend_with(ParitySetClient::new(
+					handler
+						.extend_with(ParityAccountsClient::new(&self.secret_store).to_delegate());
+				}
+				Api::ParitySet => handler.extend_with(
+					ParitySetClient::new(
 						&self.client,
 						&self.miner,
 						&self.updater,
 						&self.net_service,
 						self.fetch.clone(),
-					).to_delegate())
-				},
-				Api::Traces => {
-					handler.extend_with(TracesClient::new(&self.client).to_delegate())
-				},
+					).to_delegate(),
+				),
+				Api::Traces => handler.extend_with(TracesClient::new(&self.client).to_delegate()),
 				Api::Rpc => {
 					let modules = to_modules(&apis);
 					handler.extend_with(RpcClient::new(modules).to_delegate());
-				},
+				}
 				Api::SecretStore => {
 					handler.extend_with(SecretStoreClient::new(&self.secret_store).to_delegate());
-				},
+				}
 				Api::Whisper => {
 					if let Some(ref whisper_rpc) = self.whisper_rpc {
 						let whisper = whisper_rpc.make_handler(self.net.clone());
@@ -386,15 +428,18 @@ impl FullDependencies {
 					if !for_generic_pubsub {
 						if let Some(ref whisper_rpc) = self.whisper_rpc {
 							let whisper = whisper_rpc.make_handler(self.net.clone());
-							handler.extend_with(
-								::parity_whisper::rpc::WhisperPubSub::to_delegate(whisper)
-							);
+							handler.extend_with(::parity_whisper::rpc::WhisperPubSub::to_delegate(
+								whisper,
+							));
 						}
 					}
-				},
+				}
 				Api::Private => {
-					handler.extend_with(PrivateClient::new(self.private_tx_service.as_ref().map(|p| p.provider())).to_delegate());
-				},
+					handler.extend_with(
+						PrivateClient::new(self.private_tx_service.as_ref().map(|p| p.provider()))
+							.to_delegate(),
+					);
+				}
 			}
 		}
 	}
@@ -409,11 +454,10 @@ impl Dependencies for FullDependencies {
 		}
 	}
 
-	fn extend_with_set<S>(
-		&self,
-		handler: &mut MetaIoHandler<Metadata, S>,
-		apis: &HashSet<Api>,
-	) where S: core::Middleware<Metadata> {
+	fn extend_with_set<S>(&self, handler: &mut MetaIoHandler<Metadata, S>, apis: &HashSet<Api>)
+	where
+		S: core::Middleware<Metadata>,
+	{
 		self.extend_api(handler, apis, false)
 	}
 }
@@ -463,40 +507,44 @@ impl<C: LightChainClient + 'static> LightDependencies<C> {
 			self.on_demand.clone(),
 			self.cache.clone(),
 			self.transaction_queue.clone(),
-			Arc::new(Mutex::new(dispatch::Reservations::new(self.executor.clone()))),
+			Arc::new(Mutex::new(dispatch::Reservations::new(
+				self.executor.clone(),
+			))),
 			self.gas_price_percentile,
 		);
 
 		macro_rules! add_signing_methods {
-			($namespace:ident, $handler:expr, $deps:expr) => {
-				{
-					let deps = &$deps;
-					let dispatcher = dispatcher.clone();
-					let secret_store = deps.secret_store.clone();
-					if deps.signer_service.is_enabled() {
-						$handler.extend_with($namespace::to_delegate(
-							SigningQueueClient::new(&deps.signer_service, dispatcher, deps.executor.clone(), &secret_store)
-						))
-					} else {
-						$handler.extend_with(
-							$namespace::to_delegate(SigningUnsafeClient::new(&secret_store, dispatcher))
-						)
+			($namespace:ident, $handler:expr, $deps:expr) => {{
+				let deps = &$deps;
+				let dispatcher = dispatcher.clone();
+				let secret_store = deps.secret_store.clone();
+				if deps.signer_service.is_enabled() {
+					$handler.extend_with($namespace::to_delegate(SigningQueueClient::new(
+						&deps.signer_service,
+						dispatcher,
+						deps.executor.clone(),
+						&secret_store,
+					)))
+				} else {
+					$handler.extend_with($namespace::to_delegate(SigningUnsafeClient::new(
+						&secret_store,
+						dispatcher,
+					)))
 					}
-				}
-			}
+				}};
 		}
 
 		for api in apis {
 			match *api {
 				Api::Debug => {
 					warn!(target: "rpc", "Debug API is not available in light client mode.")
-				},
+				}
 				Api::Web3 => {
 					handler.extend_with(Web3Client::new().to_delegate());
-				},
+				}
 				Api::Net => {
 					handler.extend_with(light::NetClient::new(self.sync.clone()).to_delegate());
-				},
+				}
 				Api::Eth => {
 					let client = light::EthClient::new(
 						self.sync.clone(),
@@ -514,7 +562,7 @@ impl<C: LightChainClient + 'static> LightDependencies<C> {
 						handler.extend_with(EthFilter::to_delegate(client));
 						add_signing_methods!(EthSigning, handler, self);
 					}
-				},
+				}
 				Api::EthPubSub => {
 					let client = EthPubSubClient::light(
 						self.client.clone(),
@@ -526,77 +574,98 @@ impl<C: LightChainClient + 'static> LightDependencies<C> {
 					);
 					self.client.add_listener(client.handler() as Weak<_>);
 					let h = client.handler();
-					self.transaction_queue.write().add_listener(Box::new(move |transactions| {
-						if let Some(h) = h.upgrade() {
-							h.notify_new_transactions(transactions);
-						}
-					}));
+					self.transaction_queue
+						.write()
+						.add_listener(Box::new(move |transactions| {
+							if let Some(h) = h.upgrade() {
+								h.notify_new_transactions(transactions);
+							}
+						}));
 					handler.extend_with(EthPubSub::to_delegate(client));
-				},
+				}
 				Api::Personal => {
-					handler.extend_with(PersonalClient::new(&self.secret_store, dispatcher.clone(), self.geth_compatibility, self.experimental_rpcs).to_delegate());
-				},
+					handler.extend_with(
+						PersonalClient::new(
+							&self.secret_store,
+							dispatcher.clone(),
+							self.geth_compatibility,
+							self.experimental_rpcs,
+						).to_delegate(),
+					);
+				}
 				Api::Signer => {
-					handler.extend_with(SignerClient::new(&self.secret_store, dispatcher.clone(), &self.signer_service, self.executor.clone()).to_delegate());
-				},
+					handler.extend_with(
+						SignerClient::new(
+							&self.secret_store,
+							dispatcher.clone(),
+							&self.signer_service,
+							self.executor.clone(),
+						).to_delegate(),
+					);
+				}
 				Api::Parity => {
 					let signer = match self.signer_service.is_enabled() {
 						true => Some(self.signer_service.clone()),
 						false => None,
 					};
-					handler.extend_with(light::ParityClient::new(
-						Arc::new(dispatcher.clone()),
-						self.secret_store.clone(),
-						self.logger.clone(),
-						self.settings.clone(),
-						signer,
-						self.ws_address.clone(),
-						self.gas_price_percentile,
-					).to_delegate());
+					handler.extend_with(
+						light::ParityClient::new(
+							Arc::new(dispatcher.clone()),
+							self.secret_store.clone(),
+							self.logger.clone(),
+							self.settings.clone(),
+							signer,
+							self.ws_address.clone(),
+							self.gas_price_percentile,
+						).to_delegate(),
+					);
 
 					if !for_generic_pubsub {
 						add_signing_methods!(ParitySigning, handler, self);
 					}
-				},
+				}
 				Api::ParityPubSub => {
 					if !for_generic_pubsub {
 						let mut rpc = MetaIoHandler::default();
-						let apis = ApiSet::List(apis.clone()).retain(ApiSet::PubSub).list_apis();
+						let apis = ApiSet::List(apis.clone())
+							.retain(ApiSet::PubSub)
+							.list_apis();
 						self.extend_api(&mut rpc, &apis, true);
-						handler.extend_with(PubSubClient::new(rpc, self.executor.clone()).to_delegate());
+						handler.extend_with(
+							PubSubClient::new(rpc, self.executor.clone()).to_delegate(),
+						);
 					}
-				},
+				}
 				Api::ParityAccounts => {
-					handler.extend_with(ParityAccountsClient::new(&self.secret_store).to_delegate());
-				},
-				Api::ParitySet => {
-					handler.extend_with(light::ParitySetClient::new(
-						self.sync.clone(),
-						self.fetch.clone(),
-					).to_delegate())
-				},
-				Api::Traces => {
-					handler.extend_with(light::TracesClient.to_delegate())
-				},
+					handler
+						.extend_with(ParityAccountsClient::new(&self.secret_store).to_delegate());
+				}
+				Api::ParitySet => handler.extend_with(
+					light::ParitySetClient::new(self.sync.clone(), self.fetch.clone())
+						.to_delegate(),
+				),
+				Api::Traces => handler.extend_with(light::TracesClient.to_delegate()),
 				Api::Rpc => {
 					let modules = to_modules(&apis);
 					handler.extend_with(RpcClient::new(modules).to_delegate());
-				},
+				}
 				Api::SecretStore => {
 					handler.extend_with(SecretStoreClient::new(&self.secret_store).to_delegate());
-				},
+				}
 				Api::Whisper => {
 					if let Some(ref whisper_rpc) = self.whisper_rpc {
 						let whisper = whisper_rpc.make_handler(self.net.clone());
 						handler.extend_with(::parity_whisper::rpc::Whisper::to_delegate(whisper));
 					}
-				},
+				}
 				Api::WhisperPubSub => {
 					if let Some(ref whisper_rpc) = self.whisper_rpc {
 						let whisper = whisper_rpc.make_handler(self.net.clone());
-						handler.extend_with(::parity_whisper::rpc::WhisperPubSub::to_delegate(whisper));
+						handler.extend_with(::parity_whisper::rpc::WhisperPubSub::to_delegate(
+							whisper,
+						));
 					}
-				},
+				}
 				Api::Private => {
 					if let Some(ref tx_manager) = self.private_tx_service {
 						let private_tx_service = Some(tx_manager.clone());
@@ -611,13 +680,14 @@ impl<C: LightChainClient + 'static> LightDependencies<C> {
 impl<T: LightChainClient + 'static> Dependencies for LightDependencies<T> {
 	type Notifier = LightClientNotifier;
 
-	fn activity_notifier(&self) -> Self::Notifier { LightClientNotifier }
+	fn activity_notifier(&self) -> Self::Notifier {
+		LightClientNotifier
+	}
 
-	fn extend_with_set<S>(
-		&self,
-		handler: &mut MetaIoHandler<Metadata, S>,
-		apis: &HashSet<Api>,
-	) where S: core::Middleware<Metadata> {
+	fn extend_with_set<S>(&self, handler: &mut MetaIoHandler<Metadata, S>, apis: &HashSet<Api>)
+	where
+		S: core::Middleware<Metadata>,
+	{
 		self.extend_api(handler, apis, false)
 	}
 }
@@ -639,7 +709,10 @@ impl ApiSet {
 			Api::Whisper,
 			Api::WhisperPubSub,
 			Api::Private,
-		].into_iter().cloned().collect();
+		]
+			.into_iter()
+			.cloned()
+			.collect();
 
 		match *self {
 			ApiSet::List(ref apis) => apis.clone(),
@@ -647,13 +720,13 @@ impl ApiSet {
 				public_list.insert(Api::Traces);
 				public_list.insert(Api::ParityPubSub);
 				public_list
-			},
+			}
 			ApiSet::IpcContext => {
 				public_list.insert(Api::Traces);
 				public_list.insert(Api::ParityPubSub);
 				public_list.insert(Api::ParityAccounts);
 				public_list
-			},
+			}
 			ApiSet::SafeContext => {
 				public_list.insert(Api::Debug);
 				public_list.insert(Api::Traces);
@@ -663,7 +736,7 @@ impl ApiSet {
 				public_list.insert(Api::Signer);
 				public_list.insert(Api::SecretStore);
 				public_list
-			},
+			}
 			ApiSet::All => {
 				public_list.insert(Api::Debug);
 				public_list.insert(Api::Traces);
@@ -674,14 +747,17 @@ impl ApiSet {
 				public_list.insert(Api::Personal);
 				public_list.insert(Api::SecretStore);
 				public_list
-			},
+			}
 			ApiSet::PubSub => [
 				Api::Eth,
 				Api::Parity,
 				Api::ParityAccounts,
 				Api::ParitySet,
 				Api::Traces,
-			].into_iter().cloned().collect()
+			]
+				.into_iter()
+				.cloned()
+				.collect(),
 		}
 	}
 }
@@ -718,15 +794,29 @@ mod test {
 
 	#[test]
 	fn test_api_set_parsing() {
-		assert_eq!(ApiSet::List(vec![Api::Web3, Api::Eth].into_iter().collect()), "web3,eth".parse().unwrap());
+		assert_eq!(
+			ApiSet::List(vec![Api::Web3, Api::Eth].into_iter().collect()),
+			"web3,eth".parse().unwrap()
+		);
 	}
 
 	#[test]
 	fn test_api_set_unsafe_context() {
 		let expected = vec![
 			// make sure this list contains only SAFE methods
-			Api::Web3, Api::Net, Api::Eth, Api::EthPubSub, Api::Parity, Api::ParityPubSub, Api::Traces, Api::Rpc, Api::Whisper, Api::WhisperPubSub, Api::Private,
-		].into_iter().collect();
+			Api::Web3,
+			Api::Net,
+			Api::Eth,
+			Api::EthPubSub,
+			Api::Parity,
+			Api::ParityPubSub,
+			Api::Traces,
+			Api::Rpc,
+			Api::Whisper,
+			Api::WhisperPubSub,
+			Api::Private,
+		].into_iter()
+		.collect();
 		assert_eq!(ApiSet::UnsafeContext.list_apis(), expected);
 	}
 
@@ -734,10 +824,21 @@ mod test {
 	fn test_api_set_ipc_context() {
 		let expected = vec![
 			// safe
-			Api::Web3, Api::Net, Api::Eth, Api::EthPubSub, Api::Parity, Api::ParityPubSub, Api::Traces, Api::Rpc, Api::Whisper, Api::WhisperPubSub, Api::Private,
+			Api::Web3,
+			Api::Net,
+			Api::Eth,
+			Api::EthPubSub,
+			Api::Parity,
+			Api::ParityPubSub,
+			Api::Traces,
+			Api::Rpc,
+			Api::Whisper,
+			Api::WhisperPubSub,
+			Api::Private,
 			// semi-safe
-			Api::ParityAccounts
-		].into_iter().collect();
+			Api::ParityAccounts,
+		].into_iter()
+		.collect();
 		assert_eq!(ApiSet::IpcContext.list_apis(), expected);
 	}
 
@@ -745,41 +846,106 @@ mod test {
 	fn test_api_set_safe_context() {
 		let expected = vec![
 			// safe
-			Api::Web3, Api::Net, Api::Eth, Api::EthPubSub, Api::Parity, Api::ParityPubSub, Api::Traces, Api::Rpc, Api::SecretStore, Api::Whisper, Api::WhisperPubSub, Api::Private,
+			Api::Web3,
+			Api::Net,
+			Api::Eth,
+			Api::EthPubSub,
+			Api::Parity,
+			Api::ParityPubSub,
+			Api::Traces,
+			Api::Rpc,
+			Api::SecretStore,
+			Api::Whisper,
+			Api::WhisperPubSub,
+			Api::Private,
 			// semi-safe
 			Api::ParityAccounts,
 			// Unsafe
-			Api::ParitySet, Api::Signer, Api::Debug
-		].into_iter().collect();
+			Api::ParitySet,
+			Api::Signer,
+			Api::Debug,
+		].into_iter()
+		.collect();
 		assert_eq!(ApiSet::SafeContext.list_apis(), expected);
 	}
 
 	#[test]
 	fn test_all_apis() {
-		assert_eq!("all".parse::<ApiSet>().unwrap(), ApiSet::List(vec![
-			Api::Web3, Api::Net, Api::Eth, Api::EthPubSub, Api::Parity, Api::ParityPubSub, Api::Traces, Api::Rpc, Api::SecretStore, Api::Whisper, Api::WhisperPubSub,
-			Api::ParityAccounts,
-			Api::ParitySet, Api::Signer,
-			Api::Personal,
-			Api::Private,
-			Api::Debug,
-		].into_iter().collect()));
+		assert_eq!(
+			"all".parse::<ApiSet>().unwrap(),
+			ApiSet::List(
+				vec![
+					Api::Web3,
+					Api::Net,
+					Api::Eth,
+					Api::EthPubSub,
+					Api::Parity,
+					Api::ParityPubSub,
+					Api::Traces,
+					Api::Rpc,
+					Api::SecretStore,
+					Api::Whisper,
+					Api::WhisperPubSub,
+					Api::ParityAccounts,
+					Api::ParitySet,
+					Api::Signer,
+					Api::Personal,
+					Api::Private,
+					Api::Debug,
+				].into_iter()
+				.collect()
+			)
+		);
 	}
 
 	#[test]
 	fn test_all_without_personal_apis() {
-		assert_eq!("personal,all,-personal".parse::<ApiSet>().unwrap(), ApiSet::List(vec![
-			Api::Web3, Api::Net, Api::Eth, Api::EthPubSub, Api::Parity, Api::ParityPubSub, Api::Traces, Api::Rpc, Api::SecretStore, Api::Whisper, Api::WhisperPubSub,
-			Api::ParityAccounts,
-			Api::ParitySet, Api::Signer,
-			Api::Private, Api::Debug,
-		].into_iter().collect()));
+		assert_eq!(
+			"personal,all,-personal".parse::<ApiSet>().unwrap(),
+			ApiSet::List(
+				vec![
+					Api::Web3,
+					Api::Net,
+					Api::Eth,
+					Api::EthPubSub,
+					Api::Parity,
+					Api::ParityPubSub,
+					Api::Traces,
+					Api::Rpc,
+					Api::SecretStore,
+					Api::Whisper,
+					Api::WhisperPubSub,
+					Api::ParityAccounts,
+					Api::ParitySet,
+					Api::Signer,
+					Api::Private,
+					Api::Debug,
+				].into_iter()
+				.collect()
+			)
+		);
 	}
 
 	#[test]
 	fn test_safe_parsing() {
-		assert_eq!("safe".parse::<ApiSet>().unwrap(), ApiSet::List(vec![
-			Api::Web3, Api::Net, Api::Eth, Api::EthPubSub, Api::Parity, Api::ParityPubSub, Api::Traces, Api::Rpc, Api::Whisper, Api::WhisperPubSub, Api::Private,
-		].into_iter().collect()));
+		assert_eq!(
+			"safe".parse::<ApiSet>().unwrap(),
+			ApiSet::List(
+				vec![
+					Api::Web3,
+					Api::Net,
+					Api::Eth,
+					Api::EthPubSub,
+					Api::Parity,
+					Api::ParityPubSub,
+					Api::Traces,
+					Api::Rpc,
+					Api::Whisper,
+					Api::WhisperPubSub,
+					Api::Private,
+				].into_iter()
+				.collect()
+			)
+		);
 	}
 }
diff --git a/parity/run.rs b/parity/run.rs
index 3a7299df3..4d5d371b4 100644
--- a/parity/run.rs
+++ b/parity/run.rs
@@ -127,6 +127,7 @@ pub struct RunCmd {
 	pub stratum: Option<stratum::Options>,
 	pub snapshot_conf: SnapshotConfiguration,
 	pub check_seal: bool,
+	pub allow_missing_blocks: bool,
 	pub download_old_blocks: bool,
 	pub verifier_settings: VerifierSettings,
 	pub serve_light: bool,
@@ -717,6 +718,7 @@ fn execute_impl<Cr, Rr>(cmd: RunCmd, logger: Arc<RotatingLogger>, on_client_rq:
 		private_tx_service: Some(private_tx_service.clone()),
 		gas_price_percentile: cmd.gas_price_percentile,
 		poll_lifetime: cmd.poll_lifetime,
+		allow_missing_blocks: cmd.allow_missing_blocks,
 	});
 
 	let dependencies = rpc::Dependencies {
diff --git a/rpc/src/v1/helpers/errors.rs b/rpc/src/v1/helpers/errors.rs
index b1e11f580..d4bfff742 100644
--- a/rpc/src/v1/helpers/errors.rs
+++ b/rpc/src/v1/helpers/errors.rs
@@ -18,15 +18,18 @@
 
 use std::fmt;
 
-use ethcore::account_provider::{SignError as AccountError};
+use ethcore::account_provider::SignError as AccountError;
 use ethcore::error::{Error as EthcoreError, ErrorKind, CallError};
 use ethcore::client::BlockId;
-use jsonrpc_core::{futures, Error, ErrorCode, Value};
+use jsonrpc_core::{futures, Result as RpcResult, Error, ErrorCode, Value};
 use rlp::DecoderError;
 use transaction::Error as TransactionError;
 use ethcore_private_tx::Error as PrivateTransactionError;
 use vm::Error as VMError;
 use light::on_demand::error::{Error as OnDemandError, ErrorKind as OnDemandErrorKind};
+use ethcore::client::BlockChainClient;
+use ethcore::blockchain_info::BlockChainInfo;
+use v1::types::BlockNumber;
 
 mod codes {
 	// NOTE [ToDr] Codes from [-32099, -32000]
@@ -208,6 +211,60 @@ pub fn cannot_submit_work(err: EthcoreError) -> Error {
 	}
 }
 
+pub fn unavailable_block() -> Error {
+	Error {
+		code: ErrorCode::ServerError(codes::UNSUPPORTED_REQUEST),
+		message: "Ancient block sync is still in progress".into(),
+		data: None,
+	}
+}
+
+pub fn check_block_number_existence<'a, T, C>(
+	client: &'a C,
+	num: BlockNumber,
+	allow_missing_blocks: bool,
+) ->
+	impl Fn(Option<T>) -> RpcResult<Option<T>> + 'a
+	where C: BlockChainClient,
+{
+	move |response| {
+		if response.is_none() {
+			if let BlockNumber::Num(block_number) = num {
+				// tried to fetch block number and got nothing even though the block number is
+				// less than the latest block number
+				if block_number < client.chain_info().best_block_number && !allow_missing_blocks {
+					return Err(unavailable_block());
+				}
+			}
+		}
+		Ok(response)
+	}
+}
+
+pub fn check_block_gap<'a, T, C>(
+	client: &'a C,
+	allow_missing_blocks: bool,
+) -> impl Fn(Option<T>) -> RpcResult<Option<T>> + 'a
+	where C: BlockChainClient,
+{
+	move |response| {
+		if response.is_none() && !allow_missing_blocks {
+			let BlockChainInfo { ancient_block_hash, .. } = client.chain_info();
+			// block information was requested, but unfortunately we couldn't find it and there
+			// are gaps in the database ethcore/src/blockchain/blockchain.rs
+			if ancient_block_hash.is_some() {
+				return Err(Error {
+					code: ErrorCode::ServerError(codes::UNSUPPORTED_REQUEST),
+					message: "Block information is incomplete while ancient block sync is still in progress, before \
+					it's finished we can't determine the existence of requested item.".into(),
+					data: None,
+				})
+			}
+		}
+		Ok(response)
+	}
+}
+
 pub fn not_enough_data() -> Error {
 	Error {
 		code: ErrorCode::ServerError(codes::UNSUPPORTED_REQUEST),
@@ -328,22 +385,22 @@ pub fn transaction_message(error: &TransactionError) -> String {
 		Old => "Transaction nonce is too low. Try incrementing the nonce.".into(),
 		TooCheapToReplace => {
 			"Transaction gas price is too low. There is another transaction with same nonce in the queue. Try increasing the gas price or incrementing the nonce.".into()
-		},
+		}
 		LimitReached => {
 			"There are too many transactions in the queue. Your transaction was dropped due to limit. Try increasing the fee.".into()
-		},
+		}
 		InsufficientGas { minimal, got } => {
 			format!("Transaction gas is too low. There is not enough gas to cover minimal cost of the transaction (minimal: {}, got: {}). Try increasing supplied gas.", minimal, got)
-		},
+		}
 		InsufficientGasPrice { minimal, got } => {
 			format!("Transaction gas price is too low. It does not satisfy your node's minimal gas price (minimal: {}, got: {}). Try increasing the gas price.", minimal, got)
-		},
+		}
 		InsufficientBalance { balance, cost } => {
 			format!("Insufficient funds. The account you tried to send transaction from does not have enough funds. Required {} and got: {}.", cost, balance)
-		},
+		}
 		GasLimitExceeded { limit, got } => {
 			format!("Transaction cost exceeds current gas limit. Limit: {}, got: {}. Try decreasing supplied gas.", limit, got)
-		},
+		}
 		InvalidSignature(ref sig) => format!("Invalid signature: {}", sig),
 		InvalidChainId => "Invalid chain id.".into(),
 		InvalidGasLimit(_) => "Supplied gas is beyond limit.".into(),
@@ -382,7 +439,6 @@ pub fn decode<T: Into<EthcoreError>>(error: T) -> Error {
 			message: "decoding error".into(),
 			data: None,
 		}
-
 	}
 }
 
diff --git a/rpc/src/v1/impls/eth.rs b/rpc/src/v1/impls/eth.rs
index 821745600..3a2e58040 100644
--- a/rpc/src/v1/impls/eth.rs
+++ b/rpc/src/v1/impls/eth.rs
@@ -65,6 +65,9 @@ pub struct EthClientOptions {
 	pub send_block_number_in_get_work: bool,
 	/// Gas Price Percentile used as default gas price.
 	pub gas_price_percentile: usize,
+	/// Return 'null' instead of an error if ancient block sync is still in
+	/// progress and the block information requested could not be found.
+	pub allow_missing_blocks: bool,
 	/// Enable Experimental RPC-Calls
 	pub allow_experimental_rpcs: bool,
 }
@@ -86,6 +89,7 @@ impl Default for EthClientOptions {
 			allow_pending_receipt_query: true,
 			send_block_number_in_get_work: true,
 			gas_price_percentile: 50,
+			allow_missing_blocks: false,
 			allow_experimental_rpcs: false,
 		}
 	}
@@ -645,30 +649,51 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM, T: StateInfo + 'static> Eth for EthClient<
 	}
 
 	fn block_transaction_count_by_hash(&self, hash: RpcH256) -> BoxFuture<Option<RpcU256>> {
-		Box::new(future::ok(self.client.block(BlockId::Hash(hash.into()))
-			.map(|block| block.transactions_count().into())))
+		let trx_count = self.client.block(BlockId::Hash(hash.into()))
+			.map(|block| block.transactions_count().into());
+		let result = Ok(trx_count)
+			.and_then(errors::check_block_gap(&*self.client, self.options.allow_missing_blocks));
+		Box::new(future::done(result))
 	}
 
 	fn block_transaction_count_by_number(&self, num: BlockNumber) -> BoxFuture<Option<RpcU256>> {
-		Box::new(future::ok(match num {
+		Box::new(future::done(match num {
 			BlockNumber::Pending =>
-				Some(self.miner.pending_transaction_hashes(&*self.client).len().into()),
-			_ =>
-				self.client.block(block_number_to_id(num)).map(|block| block.transactions_count().into())
+				Ok(Some(self.miner.pending_transaction_hashes(&*self.client).len().into())),
+			_ => {
+				let trx_count = self.client.block(block_number_to_id(num.clone()))
+					.map(|block| block.transactions_count().into());
+				Ok(trx_count)
+					.and_then(errors::check_block_number_existence(
+						&*self.client,
+						num,
+						self.options.allow_missing_blocks
+					))
+			}
 		}))
 	}
 
 	fn block_uncles_count_by_hash(&self, hash: RpcH256) -> BoxFuture<Option<RpcU256>> {
-		Box::new(future::ok(self.client.block(BlockId::Hash(hash.into()))
-			.map(|block| block.uncles_count().into())))
+		let uncle_count = self.client.block(BlockId::Hash(hash.into()))
+			.map(|block| block.uncles_count().into());
+		let result = Ok(uncle_count)
+			.and_then(errors::check_block_gap(&*self.client, self.options.allow_missing_blocks));
+		Box::new(future::done(result))
 	}
 
 	fn block_uncles_count_by_number(&self, num: BlockNumber) -> BoxFuture<Option<RpcU256>> {
-		Box::new(future::ok(match num {
-			BlockNumber::Pending => Some(0.into()),
-			_ => self.client.block(block_number_to_id(num))
-					.map(|block| block.uncles_count().into()
-			),
+		Box::new(future::done(match num {
+			BlockNumber::Pending => Ok(Some(0.into())),
+			_ => {
+				let uncles_count = self.client.block(block_number_to_id(num.clone()))
+					.map(|block| block.uncles_count().into());
+				Ok(uncles_count)
+					.and_then(errors::check_block_number_existence(
+						&*self.client,
+						num,
+						self.options.allow_missing_blocks
+					))
+			}
 		}))
 	}
 
@@ -687,11 +712,15 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM, T: StateInfo + 'static> Eth for EthClient<
 	}
 
 	fn block_by_hash(&self, hash: RpcH256, include_txs: bool) -> BoxFuture<Option<RichBlock>> {
-		Box::new(future::done(self.rich_block(BlockId::Hash(hash.into()).into(), include_txs)))
+		let result = self.rich_block(BlockId::Hash(hash.into()).into(), include_txs)
+			.and_then(errors::check_block_gap(&*self.client, self.options.allow_missing_blocks));
+		Box::new(future::done(result))
 	}
 
 	fn block_by_number(&self, num: BlockNumber, include_txs: bool) -> BoxFuture<Option<RichBlock>> {
-		Box::new(future::done(self.rich_block(num.into(), include_txs)))
+		let result = self.rich_block(num.clone().into(), include_txs).and_then(
+			errors::check_block_number_existence(&*self.client, num, self.options.allow_missing_blocks));
+		Box::new(future::done(result))
 	}
 
 	fn transaction_by_hash(&self, hash: RpcH256) -> BoxFuture<Option<Transaction>> {
@@ -700,13 +729,16 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM, T: StateInfo + 'static> Eth for EthClient<
 			self.miner.transaction(&hash)
 				.map(|t| Transaction::from_pending(t.pending().clone()))
 		});
-
-		Box::new(future::ok(tx))
+		let result = Ok(tx).and_then(
+			errors::check_block_gap(&*self.client, self.options.allow_missing_blocks));
+		Box::new(future::done(result))
 	}
 
 	fn transaction_by_block_hash_and_index(&self, hash: RpcH256, index: Index) -> BoxFuture<Option<Transaction>> {
 		let id = PendingTransactionId::Location(PendingOrBlock::Block(BlockId::Hash(hash.into())), index.value());
-		Box::new(future::done(self.transaction(id)))
+		let result = self.transaction(id).and_then(
+			errors::check_block_gap(&*self.client, self.options.allow_missing_blocks));
+		Box::new(future::done(result))
 	}
 
 	fn transaction_by_block_number_and_index(&self, num: BlockNumber, index: Index) -> BoxFuture<Option<Transaction>> {
@@ -718,7 +750,9 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM, T: StateInfo + 'static> Eth for EthClient<
 		};
 
 		let transaction_id = PendingTransactionId::Location(block_id, index.value());
-		Box::new(future::done(self.transaction(transaction_id)))
+		let result = self.transaction(transaction_id).and_then(
+			errors::check_block_number_existence(&*self.client, num, self.options.allow_missing_blocks));
+		Box::new(future::done(result))
 	}
 
 	fn transaction_receipt(&self, hash: RpcH256) -> BoxFuture<Option<Receipt>> {
@@ -732,14 +766,17 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM, T: StateInfo + 'static> Eth for EthClient<
 		}
 
 		let receipt = self.client.transaction_receipt(TransactionId::Hash(hash));
-		Box::new(future::ok(receipt.map(Into::into)))
+		let result = Ok(receipt.map(Into::into))
+			.and_then(errors::check_block_gap(&*self.client, self.options.allow_missing_blocks));
+		Box::new(future::done(result))
 	}
 
 	fn uncle_by_block_hash_and_index(&self, hash: RpcH256, index: Index) -> BoxFuture<Option<RichBlock>> {
-		Box::new(future::done(self.uncle(PendingUncleId {
+		let result = self.uncle(PendingUncleId {
 			id: PendingOrBlock::Block(BlockId::Hash(hash.into())),
 			position: index.value()
-		})))
+		}).and_then(errors::check_block_gap(&*self.client, self.options.allow_missing_blocks));
+		Box::new(future::done(result))
 	}
 
 	fn uncle_by_block_number_and_index(&self, num: BlockNumber, index: Index) -> BoxFuture<Option<RichBlock>> {
@@ -751,7 +788,14 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM, T: StateInfo + 'static> Eth for EthClient<
 			BlockNumber::Pending => PendingUncleId { id: PendingOrBlock::Pending, position: index.value() },
 		};
 
-		Box::new(future::done(self.uncle(id)))
+		let result = self.uncle(id)
+			.and_then(errors::check_block_number_existence(
+				&*self.client,
+				num,
+				self.options.allow_missing_blocks
+			));
+
+		Box::new(future::done(result))
 	}
 
 	fn compilers(&self) -> Result<Vec<String>> {
diff --git a/rpc/src/v1/tests/eth.rs b/rpc/src/v1/tests/eth.rs
index b0c599aa8..9a7bb19b1 100644
--- a/rpc/src/v1/tests/eth.rs
+++ b/rpc/src/v1/tests/eth.rs
@@ -146,6 +146,7 @@ impl EthTester {
 				send_block_number_in_get_work: true,
 				gas_price_percentile: 50,
 				allow_experimental_rpcs: true,
+				allow_missing_blocks: false
 			},
 		);