diff --git a/substrate/executor/src/wasm_executor.rs b/substrate/executor/src/wasm_executor.rs
index 580da80772..b12986e975 100644
--- a/substrate/executor/src/wasm_executor.rs
+++ b/substrate/executor/src/wasm_executor.rs
@@ -208,6 +208,8 @@ mod tests {
 		fn set_storage(&mut self, key: Vec<u8>, value: Vec<u8>) {
 			self.storage.insert(key, value);
 		}
+
+		fn chain_id(&self) -> u64 { 42 }
 	}
 
 	#[test]
diff --git a/substrate/state_machine/src/lib.rs b/substrate/state_machine/src/lib.rs
index 3ff3b69469..e94b2b6078 100644
--- a/substrate/state_machine/src/lib.rs
+++ b/substrate/state_machine/src/lib.rs
@@ -131,7 +131,7 @@ pub trait Externalities {
 	fn set_storage(&mut self, key: Vec<u8>, value: Vec<u8>);
 
 	/// Get the identity of the chain.
-	fn chain_id(&self) -> u64 { 42 }	// TODO: remove implementation and fix resulting errors.
+	fn chain_id(&self) -> u64;
 
 	/// Get the current set of authorities from storage.
 	fn authorities(&self) -> Result<Vec<&[u8]>, Self::Error> {
@@ -244,6 +244,8 @@ mod tests {
 		fn set_storage(&mut self, key: Vec<u8>, value: Vec<u8>) {
 			self.storage.insert(key, value);
 		}
+		
+		fn chain_id(&self) -> u64 { 42 }
 	}
 
 	#[test]
diff --git a/substrate/wasm-runtime/polkadot/src/support/testing.rs b/substrate/wasm-runtime/polkadot/src/support/testing.rs
index d73917eb16..ec7fac6d6d 100644
--- a/substrate/wasm-runtime/polkadot/src/support/testing.rs
+++ b/substrate/wasm-runtime/polkadot/src/support/testing.rs
@@ -16,4 +16,6 @@ impl Externalities for TestExternalities {
 	fn set_storage(&mut self, key: Vec<u8>, value: Vec<u8>) {
 		self.storage.insert(key, value);
 	}
+
+	fn chain_id(&self) -> u64 { 42 }
 }
diff --git a/substrate/wasm-runtime/polkadot/src/system.rs b/substrate/wasm-runtime/polkadot/src/system.rs
index 88414fa9a1..de8b814bcf 100644
--- a/substrate/wasm-runtime/polkadot/src/system.rs
+++ b/substrate/wasm-runtime/polkadot/src/system.rs
@@ -96,6 +96,8 @@ mod tests {
 		fn set_storage(&mut self, key: Vec<u8>, value: Vec<u8>) {
 			self.storage.insert(key, value);
 		}
+
+		fn chain_id(&self) -> u64 { 42 }
 	}
 
 	macro_rules! map {