diff --git a/ethcore/client-traits/src/lib.rs b/ethcore/client-traits/src/lib.rs
index 3bdec5fa0..829a0b425 100644
--- a/ethcore/client-traits/src/lib.rs
+++ b/ethcore/client-traits/src/lib.rs
@@ -274,7 +274,7 @@ pub trait BlockChainClient:
 
 	/// Get a list of all storage keys in the block `id`, if fat DB is in operation, otherwise `None`.
 	/// If `after` is set the list starts with the following item.
-	fn list_storage(&self, id: BlockId, account: &Address, after: Option<&H256>, count: u64) -> Option<Vec<H256>>;
+	fn list_storage(&self, id: BlockId, account: &Address, after: Option<&H256>, count: Option<u64>) -> Option<Vec<H256>>;
 
 	/// Get transaction with given hash.
 	fn transaction(&self, id: TransactionId) -> Option<LocalizedTransaction>;
diff --git a/ethcore/src/client/client.rs b/ethcore/src/client/client.rs
index 6d3e740d0..8d762155b 100644
--- a/ethcore/src/client/client.rs
+++ b/ethcore/src/client/client.rs
@@ -1805,7 +1805,7 @@ impl BlockChainClient for Client {
 		Some(accounts)
 	}
 
-	fn list_storage(&self, id: BlockId, account: &Address, after: Option<&H256>, count: u64) -> Option<Vec<H256>> {
+	fn list_storage(&self, id: BlockId, account: &Address, after: Option<&H256>, count: Option<u64>) -> Option<Vec<H256>> {
 		if !self.factories.trie.is_fat() {
 			trace!(target: "fatdb", "list_storage: Not a fat DB");
 			return None;
@@ -1846,9 +1846,16 @@ impl BlockChainClient for Client {
 			}
 		}
 
-		let keys = iter.filter_map(|item| {
-			item.ok().map(|(key, _)| H256::from_slice(&key))
-		}).take(count as usize).collect();
+		let keys = {
+			let f = iter.filter_map(|item| {
+				item.ok().map(|(key, _)| H256::from_slice(&key))
+			});
+			if let Some(count) = count {
+				f.take(count as usize).collect()
+			} else {
+				f.collect()
+			}
+		};
 
 		Some(keys)
 	}
diff --git a/ethcore/src/test_helpers/test_client.rs b/ethcore/src/test_helpers/test_client.rs
index dd34f0849..e7b579d65 100644
--- a/ethcore/src/test_helpers/test_client.rs
+++ b/ethcore/src/test_helpers/test_client.rs
@@ -735,7 +735,7 @@ impl BlockChainClient for TestBlockChainClient {
 		None
 	}
 
-	fn list_storage(&self, _id: BlockId, _account: &Address, _after: Option<&H256>, _count: u64) -> Option<Vec<H256>> {
+	fn list_storage(&self, _id: BlockId, _account: &Address, _after: Option<&H256>, _count: Option<u64>) -> Option<Vec<H256>> {
 		None
 	}
 	fn transaction(&self, _id: TransactionId) -> Option<LocalizedTransaction> {
diff --git a/parity/blockchain.rs b/parity/blockchain.rs
index 3686476c8..008da39ef 100644
--- a/parity/blockchain.rs
+++ b/parity/blockchain.rs
@@ -609,7 +609,7 @@ fn execute_export_state(cmd: ExportState) -> Result<(), String> {
 					out.write_fmt(format_args!(", \"storage\": {{")).expect("Write error");
 					let mut last_storage: Option<H256> = None;
 					loop {
-						let keys = client.list_storage(at, &account, last_storage.as_ref(), 1000).ok_or("Specified block not found")?;
+						let keys = client.list_storage(at, &account, last_storage.as_ref(), Some(1000)).ok_or("Specified block not found")?;
 						if keys.is_empty() {
 							break;
 						}
diff --git a/rpc/src/v1/impls/light/parity.rs b/rpc/src/v1/impls/light/parity.rs
index 21fe836b1..4171df78d 100644
--- a/rpc/src/v1/impls/light/parity.rs
+++ b/rpc/src/v1/impls/light/parity.rs
@@ -203,7 +203,7 @@ where
 		Err(errors::light_unimplemented(None))
 	}
 
-	fn list_storage_keys(&self, _: H160, _: u64, _: Option<H256>, _: Option<BlockNumber>) -> Result<Option<Vec<H256>>> {
+	fn list_storage_keys(&self, _: H160, _: Option<u64>, _: Option<H256>, _: Option<BlockNumber>) -> Result<Option<Vec<H256>>> {
 		Err(errors::light_unimplemented(None))
 	}
 
diff --git a/rpc/src/v1/impls/parity.rs b/rpc/src/v1/impls/parity.rs
index 2905324d6..2151ecc94 100644
--- a/rpc/src/v1/impls/parity.rs
+++ b/rpc/src/v1/impls/parity.rs
@@ -222,7 +222,7 @@ impl<C, M, U, S> Parity for ParityClient<C, M, U> where
 			.map(|a| a.into_iter().map(Into::into).collect()))
 	}
 
-	fn list_storage_keys(&self, address: H160, count: u64, after: Option<H256>, block_number: Option<BlockNumber>) -> Result<Option<Vec<H256>>> {
+	fn list_storage_keys(&self, address: H160, count: Option<u64>, after: Option<H256>, block_number: Option<BlockNumber>) -> Result<Option<Vec<H256>>> {
 		let number = match block_number.unwrap_or_default() {
 			BlockNumber::Pending => {
 				warn!("BlockNumber::Pending is unsupported");
diff --git a/rpc/src/v1/traits/parity.rs b/rpc/src/v1/traits/parity.rs
index c57b758c9..6cd09e432 100644
--- a/rpc/src/v1/traits/parity.rs
+++ b/rpc/src/v1/traits/parity.rs
@@ -117,7 +117,7 @@ pub trait Parity {
 	/// Returns all storage keys of the given address (first parameter) if Fat DB is enabled (`--fat-db`),
 	/// or null if not.
 	#[rpc(name = "parity_listStorageKeys")]
-	fn list_storage_keys(&self, H160, u64, Option<H256>, Option<BlockNumber>) -> Result<Option<Vec<H256>>>;
+	fn list_storage_keys(&self, H160, Option<u64>, Option<H256>, Option<BlockNumber>) -> Result<Option<Vec<H256>>>;
 
 	/// Encrypt some data with a public key under ECIES.
 	/// First parameter is the 512-byte destination public key, second is the message.