diff --git a/ethcore/src/client/client.rs b/ethcore/src/client/client.rs
index 00c8dd8de..c46f477b1 100644
--- a/ethcore/src/client/client.rs
+++ b/ethcore/src/client/client.rs
@@ -619,7 +619,8 @@ impl Client {
 	/// Attempt to get a copy of a specific block's final state.
 	///
 	/// This will not fail if given BlockId::Latest.
-	/// Otherwise, this can fail (but may not) if the DB prunes state.
+	/// Otherwise, this can fail (but may not) if the DB prunes state or the block
+	/// is unknown.
 	pub fn state_at(&self, id: BlockId) -> Option<State> {
 		// fast path for latest state.
 		match id.clone() {
diff --git a/ethcore/src/client/test_client.rs b/ethcore/src/client/test_client.rs
index e482b418a..075f3f11c 100644
--- a/ethcore/src/client/test_client.rs
+++ b/ethcore/src/client/test_client.rs
@@ -523,7 +523,8 @@ impl BlockChainClient for TestBlockChainClient {
 		match id {
 			BlockId::Number(number) if (number as usize) < self.blocks.read().len() => BlockStatus::InChain,
 			BlockId::Hash(ref hash) if self.blocks.read().get(hash).is_some() => BlockStatus::InChain,
-			_ => BlockStatus::Unknown
+			BlockId::Latest | BlockId::Pending | BlockId::Earliest => BlockStatus::InChain,
+			_ => BlockStatus::Unknown,
 		}
 	}
 
diff --git a/ethcore/src/client/traits.rs b/ethcore/src/client/traits.rs
index caba647d1..2d7d882ee 100644
--- a/ethcore/src/client/traits.rs
+++ b/ethcore/src/client/traits.rs
@@ -277,7 +277,7 @@ pub trait BlockChainClient : Sync + Send {
 	/// Get the address of the registry itself.
 	fn registrar_address(&self) -> Option<Address>;
 
-	/// Get the address of a particular blockchain service, if available. 
+	/// Get the address of a particular blockchain service, if available.
 	fn registry_address(&self, name: String) -> Option<Address>;
 }
 
diff --git a/rpc/src/v1/helpers/errors.rs b/rpc/src/v1/helpers/errors.rs
index 83b3b0c58..80a0dab9a 100644
--- a/rpc/src/v1/helpers/errors.rs
+++ b/rpc/src/v1/helpers/errors.rs
@@ -290,3 +290,11 @@ pub fn from_call_error(error: CallError) -> Error {
 		CallError::TransactionNotFound => internal("{}, this should not be the case with eth_call, most likely a bug.", CallError::TransactionNotFound),
 	}
 }
+
+pub fn unknown_block() -> Error {
+	Error {
+		code: ErrorCode::ServerError(codes::UNSUPPORTED_REQUEST),
+		message: "Unknown block number".into(),
+		data: None,
+	}
+}
diff --git a/rpc/src/v1/impls/eth.rs b/rpc/src/v1/impls/eth.rs
index 491bdde10..178377692 100644
--- a/rpc/src/v1/impls/eth.rs
+++ b/rpc/src/v1/impls/eth.rs
@@ -238,6 +238,15 @@ pub fn pending_logs<M>(miner: &M, best_block: EthBlockNumber, filter: &EthcoreFi
 	result
 }
 
+fn check_known<C>(client: &C, number: BlockNumber) -> Result<(), Error> where C: MiningBlockChainClient {
+	use ethcore::block_status::BlockStatus;
+
+	match client.block_status(number.into()) {
+		BlockStatus::InChain => Ok(()),
+		_ => Err(errors::unknown_block()),
+	}
+}
+
 const MAX_QUEUE_SIZE_TO_MINE_ON: usize = 4;	// because uncles go back 6.
 
 impl<C, SN: ?Sized, S: ?Sized, M, EM> EthClient<C, SN, S, M, EM> where
@@ -359,9 +368,14 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM> Eth for EthClient<C, SN, S, M, EM> where
 		let address = address.into();
 		match num.0 {
 			BlockNumber::Pending => Ok(take_weak!(self.miner).balance(&*take_weak!(self.client), &address).into()),
-			id => match take_weak!(self.client).balance(&address, id.into()) {
-				Some(balance) => Ok(balance.into()),
-				None => Err(errors::state_pruned()),
+			id => {
+				let client = take_weak!(self.client);
+
+				check_known(&*client, id.clone())?;
+				match client.balance(&address, id.into()) {
+					Some(balance) => Ok(balance.into()),
+					None => Err(errors::state_pruned()),
+				}
 			}
 		}
 	}
@@ -372,9 +386,14 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM> Eth for EthClient<C, SN, S, M, EM> where
 		let position: U256 = RpcU256::into(pos);
 		match num.0 {
 			BlockNumber::Pending => Ok(take_weak!(self.miner).storage_at(&*take_weak!(self.client), &address, &H256::from(position)).into()),
-			id => match take_weak!(self.client).storage_at(&address, &H256::from(position), id.into()) {
-				Some(s) => Ok(s.into()),
-				None => Err(errors::state_pruned()),
+			id => {
+				let client = take_weak!(self.client);
+
+				check_known(&*client, id.clone())?;
+				match client.storage_at(&address, &H256::from(position), id.into()) {
+					Some(s) => Ok(s.into()),
+					None => Err(errors::state_pruned()),
+				}
 			}
 		}
 	}
@@ -385,9 +404,14 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM> Eth for EthClient<C, SN, S, M, EM> where
 		let address: Address = RpcH160::into(address);
 		match num.0 {
 			BlockNumber::Pending => Ok(take_weak!(self.miner).nonce(&*take_weak!(self.client), &address).into()),
-			id => match take_weak!(self.client).nonce(&address, id.into()) {
-				Some(nonce) => Ok(nonce.into()),
-				None => Err(errors::state_pruned()),
+			id => {
+				let client = take_weak!(self.client);
+
+				check_known(&*client, id.clone())?;
+				match client.nonce(&address, id.into()) {
+					Some(nonce) => Ok(nonce.into()),
+					None => Err(errors::state_pruned()),
+				}
 			}
 		}
 	}
@@ -441,10 +465,15 @@ impl<C, SN: ?Sized, S: ?Sized, M, EM> Eth for EthClient<C, SN, S, M, EM> where
 		let address: Address = RpcH160::into(address);
 		match num.0 {
 			BlockNumber::Pending => Ok(take_weak!(self.miner).code(&*take_weak!(self.client), &address).map_or_else(Bytes::default, Bytes::new)),
-			_ => match take_weak!(self.client).code(&address, num.0.into()) {
-				Some(code) => Ok(code.map_or_else(Bytes::default, Bytes::new)),
-				None => Err(errors::state_pruned()),
-			},
+			id => {
+				let client = take_weak!(self.client);
+
+				check_known(&*client, id.clone())?;
+				match client.code(&address, id.into()) {
+					Some(code) => Ok(code.map_or_else(Bytes::default, Bytes::new)),
+					None => Err(errors::state_pruned()),
+				}
+			}
 		}
 	}