diff --git a/runtime/src/validate_block/implementation.rs b/runtime/src/validate_block/implementation.rs
index a1f21241f9..d616419265 100644
--- a/runtime/src/validate_block/implementation.rs
+++ b/runtime/src/validate_block/implementation.rs
@@ -23,7 +23,6 @@ use runtime_primitives::traits::{
 use executive::ExecuteBlock;
 
 use substrate_trie::{MemoryDB, read_trie_value, delta_trie_root};
-use codec::Decode;
 
 use rstd::{slice, ptr, cmp, vec::Vec, boxed::Box, mem};
 
@@ -59,6 +58,8 @@ trait Storage {
 pub fn validate_block<B: BlockT, E: ExecuteBlock<B>>(
 	mut arguments: &[u8],
 ) {
+	use codec::Decode;
+
 	let (parent_hash, block_data): (B::Hash, crate::ParachainBlockData::<B>) = Decode::decode(&mut arguments)
 		.expect("Could not decode parachain block.");
 	// TODO: Add `PolkadotInherent`.
diff --git a/runtime/src/validate_block/mod.rs b/runtime/src/validate_block/mod.rs
index c973a6798e..99adf3a086 100644
--- a/runtime/src/validate_block/mod.rs
+++ b/runtime/src/validate_block/mod.rs
@@ -57,17 +57,17 @@ macro_rules! register_validate_block_impl {
 
 			#[no_mangle]
 			unsafe fn validate_block(
-				block_data: *const u8,
-				block_data_len: u64,
+				arguments: *const u8,
+				arguments_len: u64,
 			) {
-				let block_data = $crate::slice::from_raw_parts(
-					block_data,
-					block_data_len as usize,
+				let arguments = $crate::slice::from_raw_parts(
+					arguments,
+					arguments_len as usize,
 				);
 
 				$crate::validate_block::implementation::validate_block::<
 					$block, $block_executor
-				>(block_data);
+				>(arguments);
 			}
 		}
 	};
diff --git a/runtime/src/validate_block/tests.rs b/runtime/src/validate_block/tests.rs
index ef4c81b928..4d1d336a67 100644
--- a/runtime/src/validate_block/tests.rs
+++ b/runtime/src/validate_block/tests.rs
@@ -23,7 +23,8 @@ use runtime_primitives::traits::{Block as BlockT, Header as HeaderT};
 use executor::{WasmExecutor, error::Result, wasmi::RuntimeValue::{I64, I32}};
 use test_client::{
 	TestClientBuilder, TestClient,
-	runtime::{Block, Transfer}, TestClientBuilderExt,
+	runtime::{Block, Transfer, Hash}, TestClientBuilderExt,
+	client_ext::TestClient as _,
 };
 
 use std::collections::HashMap;
@@ -33,7 +34,7 @@ use codec::Encode;
 const WASM_CODE: &[u8] =
 	include_bytes!("../../../test/runtime/wasm/target/wasm32-unknown-unknown/release/cumulus_test_runtime.compact.wasm");
 
-fn call_validate_block(block_data: ParachainBlockData<Block>) -> Result<()> {
+fn call_validate_block(parent_hash: Hash, block_data: ParachainBlockData<Block>) -> Result<()> {
 	let mut ext = TestExternalities::default();
 	WasmExecutor::new().call_with_custom_signature(
 		&mut ext,
@@ -41,13 +42,13 @@ fn call_validate_block(block_data: ParachainBlockData<Block>) -> Result<()> {
 		&WASM_CODE,
 		"validate_block",
 		|alloc| {
-			let block_data = block_data.encode();
-			let block_data_offset = alloc(&block_data)?;
+			let arguments = (parent_hash, block_data).encode();
+			let arguments_offset = alloc(&arguments)?;
 
 			Ok(
 				vec![
-					I32(block_data_offset as i32),
-					I64(block_data.len() as i64),
+					I32(arguments_offset as i32),
+					I64(arguments.len() as i64),
 				]
 			)
 		},
@@ -131,7 +132,7 @@ fn validate_block_with_no_extrinsics() {
 		witness_data,
 		witness_data_storage_root
 	);
-	call_validate_block(block_data).expect("Calls `validate_block`");
+	call_validate_block(client.genesis_hash(), block_data).expect("Calls `validate_block`");
 }
 
 #[test]
@@ -150,5 +151,5 @@ fn validate_block_with_extrinsics() {
 		witness_data,
 		witness_data_storage_root
 	);
-	call_validate_block(block_data).expect("Calls `validate_block`");
+	call_validate_block(client.genesis_hash(), block_data).expect("Calls `validate_block`");
 }
\ No newline at end of file