diff --git a/substrate/executor/src/wasm_executor.rs b/substrate/executor/src/wasm_executor.rs
index 41029424fa..580da80772 100644
--- a/substrate/executor/src/wasm_executor.rs
+++ b/substrate/executor/src/wasm_executor.rs
@@ -137,7 +137,7 @@ impl_function_executor!(this: FunctionExecutor<'e, E>,
 		} else { 0 }
 	},
 	ext_chain_id() -> u64 => {
-		42u64
+		this.ext.chain_id()
 	}
 	=> <'e, E: Externalities + 'e>
 );
diff --git a/substrate/native-runtime/support/src/lib.rs b/substrate/native-runtime/support/src/lib.rs
index 9ec5f77bdd..498081cd33 100644
--- a/substrate/native-runtime/support/src/lib.rs
+++ b/substrate/native-runtime/support/src/lib.rs
@@ -70,8 +70,9 @@ pub fn set_storage(_key: &[u8], _value: &[u8]) {
 
 /// The current relay chain identifier.
 pub fn chain_id() -> u64 {
-	// TODO: fetch from Externalities.
-	42u64
+	ext::with(|holder|
+		holder.ext.chain_id()
+	).unwrap_or(0)
 }
 
 /// Execute the given closure with global function available whose functionality routes into the
@@ -105,6 +106,8 @@ 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 {
diff --git a/substrate/state_machine/src/ext.rs b/substrate/state_machine/src/ext.rs
index ce7b9a0268..1452558ccd 100644
--- a/substrate/state_machine/src/ext.rs
+++ b/substrate/state_machine/src/ext.rs
@@ -73,4 +73,8 @@ impl<'a, B: 'a> Externalities for Ext<'a, B>
 	fn set_storage(&mut self, key: Vec<u8>, value: Vec<u8>) {
 		self.overlay.set_storage(key, value);
 	}
+
+	fn chain_id(&self) -> u64 {
+		42
+	}
 }
diff --git a/substrate/state_machine/src/lib.rs b/substrate/state_machine/src/lib.rs
index 38c481113f..3ff3b69469 100644
--- a/substrate/state_machine/src/lib.rs
+++ b/substrate/state_machine/src/lib.rs
@@ -130,7 +130,10 @@ pub trait Externalities {
 	/// Set storage of current contract being called (effective immediately).
 	fn set_storage(&mut self, key: Vec<u8>, value: Vec<u8>);
 
-	/// Get the current set of authorities.
+	/// Get the identity of the chain.
+	fn chain_id(&self) -> u64 { 42 }	// TODO: remove implementation and fix resulting errors.
+
+	/// Get the current set of authorities from storage.
 	fn authorities(&self) -> Result<Vec<&[u8]>, Self::Error> {
 		(0..self.storage(b"con\0aut\0len")?.into_iter()
 				.rev()