diff --git a/ethcore/src/client/client.rs b/ethcore/src/client/client.rs
index 13cb95afe..03353a2a4 100644
--- a/ethcore/src/client/client.rs
+++ b/ethcore/src/client/client.rs
@@ -380,6 +380,12 @@ impl Client {
 			return Err(());
 		};
 
+		let verify_external_result = self.verifier.verify_block_external(header, &block.bytes, engine);
+		if let Err(e) = verify_external_result {
+			warn!(target: "client", "Stage 4 block verification failed for #{} ({})\nError: {:?}", header.number(), header.hash(), e);
+			return Err(());
+		};
+
 		// Check if Parent is in chain
 		let chain_has_parent = chain.block_header(header.parent_hash());
 		if let Some(parent) = chain_has_parent {
diff --git a/ethcore/src/verification/canon_verifier.rs b/ethcore/src/verification/canon_verifier.rs
index 849f7caad..a5d8fe73f 100644
--- a/ethcore/src/verification/canon_verifier.rs
+++ b/ethcore/src/verification/canon_verifier.rs
@@ -34,4 +34,8 @@ impl Verifier for CanonVerifier {
 	fn verify_block_final(&self, expected: &Header, got: &Header) -> Result<(), Error> {
 		verification::verify_block_final(expected, got)
 	}
+
+	fn verify_block_external(&self, header: &Header, bytes: &[u8], engine: &Engine) -> Result<(), Error> {
+		engine.verify_block_external(header, Some(bytes))
+	}
 }
diff --git a/ethcore/src/verification/noop_verifier.rs b/ethcore/src/verification/noop_verifier.rs
index 2fcd877f5..8464ba1e2 100644
--- a/ethcore/src/verification/noop_verifier.rs
+++ b/ethcore/src/verification/noop_verifier.rs
@@ -34,4 +34,8 @@ impl Verifier for NoopVerifier {
 	fn verify_block_final(&self, _expected: &Header, _got: &Header) -> Result<(), Error> {
 		Ok(())
 	}
+
+	fn verify_block_external(&self, _header: &Header, _bytes: &[u8], _engine: &Engine) -> Result<(), Error> {
+		Ok(())
+	}
 }
diff --git a/ethcore/src/verification/verifier.rs b/ethcore/src/verification/verifier.rs
index e5dabd392..55b711c1c 100644
--- a/ethcore/src/verification/verifier.rs
+++ b/ethcore/src/verification/verifier.rs
@@ -27,4 +27,6 @@ pub trait Verifier: Send + Sync {
 	fn verify_block_family(&self, header: &Header, bytes: &[u8], engine: &Engine, bc: &BlockProvider) -> Result<(), Error>;
 	/// Do a final verification check for an enacted header vs its expected counterpart.
 	fn verify_block_final(&self, expected: &Header, got: &Header) -> Result<(), Error>;
+	/// Verify a block, inspecing external state.
+	fn verify_block_external(&self, header: &Header, bytes: &[u8], engine: &Engine) -> Result<(), Error>;
 }