diff --git a/ethcore/src/block.rs b/ethcore/src/block.rs
index 2f14d8d0ad0..56cfc1c4c14 100644
--- a/ethcore/src/block.rs
+++ b/ethcore/src/block.rs
@@ -497,7 +497,7 @@ pub(crate) fn enact(
 		last_hashes,
 		// Engine such as Clique will calculate author from extra_data.
 		// this is only important for executing contracts as the 'executive_author'.
-		engine.executive_author(&header),
+		engine.executive_author(&header)?,
 		(3141562.into(), 31415620.into()),
 		vec![],
 		is_epoch_begin,
diff --git a/ethcore/src/engines/clique/mod.rs b/ethcore/src/engines/clique/mod.rs
index 01553f76e84..efd7ece6cb3 100644
--- a/ethcore/src/engines/clique/mod.rs
+++ b/ethcore/src/engines/clique/mod.rs
@@ -153,7 +153,7 @@ impl VoteType {
 }
 
 /// Clique Engine implementation
-/// block_state_by_hash -> block state indexed by header hash.
+// block_state_by_hash -> block state indexed by header hash.
 #[cfg(not(test))]
 pub struct Clique {
 	epoch_length: u64,
@@ -688,7 +688,6 @@ impl Engine<EthereumMachine> for Clique {
 	}
 
 	// Our task here is to set difficulty
-	// TODO:(niklasad1): Return `Result<(), Error>` here instead
 	fn populate_from_parent(&self, header: &mut Header, parent: &Header) {
 		// TODO(https://github.com/paritytech/parity-ethereum/issues/10410): this is a horrible hack,
 		// it is due to the fact that enact and miner both use OpenBlock::new() which will both call
@@ -742,6 +741,8 @@ impl Engine<EthereumMachine> for Clique {
 	fn stop(&mut self) {
 		if let Some(mut s) = self.step_service.as_mut() {
 			Arc::get_mut(&mut s).map(|x| x.stop());
+		} else {
+			warn!(target: "engine", "Stopping `CliqueStepService` failed requires mutable access");
 		}
 	}
 
@@ -759,8 +760,7 @@ impl Engine<EthereumMachine> for Clique {
 		super::total_difficulty_fork_choice(new, current)
 	}
 
-	fn executive_author(&self, header: &Header) -> Address {
-		// Should have been verified now.
-		recover_creator(header).expect("Unable to extract creator.")
+	fn executive_author(&self, header: &Header) -> Result<Address, Error> {
+		recover_creator(header)
 	}
 }
diff --git a/ethcore/src/engines/mod.rs b/ethcore/src/engines/mod.rs
index fb8b53f38a9..5124f079db2 100644
--- a/ethcore/src/engines/mod.rs
+++ b/ethcore/src/engines/mod.rs
@@ -135,7 +135,7 @@ impl fmt::Display for EngineError {
 			FailedSystemCall(ref msg) => format!("Failed to make system call: {}", msg),
 			MalformedMessage(ref msg) => format!("Received malformed consensus message: {}", msg),
 			RequiresClient => format!("Call requires client but none registered"),
-			RequiresSigner => format!("Call requires client but none registered"),
+			RequiresSigner => format!("Call requires signer but none registered"),
 			InvalidEngine => format!("Invalid engine specification or implementation"),
 		};
 
@@ -462,7 +462,9 @@ pub trait Engine<M: Machine>: Sync + Send {
 	fn fork_choice(&self, new: &ExtendedHeader, best: &ExtendedHeader) -> ForkChoice;
 
 	/// Returns author should used when executing tx's for this block.
-	fn executive_author(&self, header: &Header) -> Address { *header.author() }
+	fn executive_author(&self, header: &Header) -> Result<Address, Error> {
+		Ok(*header.author())
+	}
 }
 
 /// Check whether a given block is the best block based on the default total difficulty rule.
diff --git a/json/src/spec/engine.rs b/json/src/spec/engine.rs
index 5de42eb22df..cfa1d8cafd1 100644
--- a/json/src/spec/engine.rs
+++ b/json/src/spec/engine.rs
@@ -136,7 +136,7 @@ mod tests {
 		let s = r#"{
 			"clique": {
 				"params": {
-					"peorid" : 15,
+					"period": 15,
 					"epoch": 30000
 				}
 			}