diff --git a/rpc/src/v1/impls/eth_filter.rs b/rpc/src/v1/impls/eth_filter.rs
index 369f474d7..b6e932d28 100644
--- a/rpc/src/v1/impls/eth_filter.rs
+++ b/rpc/src/v1/impls/eth_filter.rs
@@ -26,7 +26,7 @@ use util::Mutex;
 use v1::traits::EthFilter;
 use v1::types::{BlockNumber, Index, Filter, Log, H256 as RpcH256, U256 as RpcU256};
 use v1::helpers::{PollFilter, PollManager, limit_logs};
-use v1::helpers::params::{expect_no_params};
+use v1::helpers::params::expect_no_params;
 use v1::impls::eth::pending_logs;
 
 /// Eth filter rpc implementation.
diff --git a/rpc/src/v1/types/uint.rs b/rpc/src/v1/types/uint.rs
index bcd874a18..9be7b1170 100644
--- a/rpc/src/v1/types/uint.rs
+++ b/rpc/src/v1/types/uint.rs
@@ -77,6 +77,10 @@ macro_rules! impl_uint {
 							return Err(serde::Error::custom("Invalid length."));
 						}
 
+						if &value[0..2] != "0x" {
+							return Err(serde::Error::custom("Use hex encoded numbers with 0x prefix."))
+						}
+
 						$other::from_str(&value[2..]).map($name).map_err(|_| serde::Error::custom("Invalid hex value."))
 					}
 
@@ -100,6 +104,8 @@ mod tests {
 	use super::U256;
 	use serde_json;
 
+	type Res = Result<U256, serde_json::Error>;
+
 	#[test]
 	fn should_serialize_u256() {
 		let serialized1 = serde_json::to_string(&U256(0.into())).unwrap();
@@ -113,6 +119,21 @@ mod tests {
 		assert_eq!(serialized4, r#""0x100""#);
 	}
 
+	#[test]
+	fn should_fail_to_deserialize_decimals() {
+		let deserialized1: Res = serde_json::from_str(r#""""#);
+		let deserialized2: Res = serde_json::from_str(r#""0""#);
+		let deserialized3: Res = serde_json::from_str(r#""10""#);
+		let deserialized4: Res = serde_json::from_str(r#""1000000""#);
+		let deserialized5: Res = serde_json::from_str(r#""1000000000000000000""#);
+
+		assert!(deserialized1.is_err());
+		assert!(deserialized2.is_err());
+		assert!(deserialized3.is_err());
+		assert!(deserialized4.is_err());
+		assert!(deserialized5.is_err());
+	}
+
 	#[test]
 	fn should_deserialize_u256() {
 		let deserialized1: U256 = serde_json::from_str(r#""0x""#).unwrap();