diff --git a/polkadot/api/src/lib.rs b/polkadot/api/src/lib.rs
index bf747624c3..731c19a496 100644
--- a/polkadot/api/src/lib.rs
+++ b/polkadot/api/src/lib.rs
@@ -153,17 +153,30 @@ impl CheckedBlockId for CheckedId {
 	}
 }
 
-// set up the necessary scaffolding to execute the runtime.
+// set up the necessary scaffolding to execute a set of calls to the runtime.
+// this creates a new block on top of the given ID and initialises it.
 macro_rules! with_runtime {
 	($client: ident, $at: expr, $exec: expr) => {{
-		$client.state_at($at.block_id()).map_err(Error::from).and_then(|state| {
+		let parent = $at.block_id();
+		let header = Header {
+			parent_hash: $client.block_hash_from_id(parent)?.ok_or(ErrorKind::UnknownBlock(*parent))?,
+			number: $client.block_number_from_id(parent)?.ok_or(ErrorKind::UnknownBlock(*parent))? + 1,
+			state_root: Default::default(),
+			extrinsics_root: Default::default(),
+			digest: Default::default(),
+		};
+
+		$client.state_at(parent).map_err(Error::from).and_then(|state| {
 			let mut changes = Default::default();
 			let mut ext = state_machine::Ext {
 				overlay: &mut changes,
 				backend: &state,
 			};
 
-			::substrate_executor::with_native_environment(&mut ext, $exec).map_err(Into::into)
+			::substrate_executor::with_native_environment(&mut ext, || {
+				::runtime::Executive::initialise_block(&header);
+				($exec)()
+			}).map_err(Into::into)
 		})
 	}}
 }
@@ -196,16 +209,7 @@ impl<B: Backend> PolkadotApi for Client<B, NativeExecutor<LocalDispatch>>
 	}
 
 	fn duty_roster(&self, at: &CheckedId) -> Result<DutyRoster> {
-		// duty roster can only be queried at the start of a block,
-		// so we create a dummy.
-		let id = at.block_id();
-		let parent_hash = self.block_hash_from_id(id)?.ok_or(ErrorKind::UnknownBlock(*id))?;
-		let number = self.block_number_from_id(id)?.ok_or(ErrorKind::UnknownBlock(*id))? + 1;
-
-		with_runtime!(self, at, || {
-			::runtime::System::initialise(&number, &parent_hash, &Default::default());
-			::runtime::Parachains::calculate_duty_roster()
-		})
+		with_runtime!(self, at, ::runtime::Parachains::calculate_duty_roster)
 	}
 
 	fn timestamp(&self, at: &CheckedId) -> Result<Timestamp> {
@@ -422,4 +426,12 @@ mod tests {
 	fn fails_to_check_id_for_unknown_block() {
 		assert!(client().check_id(BlockId::Number(100)).is_err());
 	}
+
+	#[test]
+	fn gets_random_seed_with_genesis() {
+		let client = client();
+
+		let id = client.check_id(BlockId::Number(0)).unwrap();
+		assert!(client.random_seed(&id).is_ok());
+	}
 }
diff --git a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm
index 05ff2f4505..3f05418e5e 100644
Binary files a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm and b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.compact.wasm differ
diff --git a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm
index 4bb8fff698..4d67e2c551 100755
Binary files a/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm and b/polkadot/runtime/wasm/target/wasm32-unknown-unknown/release/polkadot_runtime.wasm differ