diff --git a/substrate/Cargo.lock b/substrate/Cargo.lock
index b4783a191c..c139749441 100644
--- a/substrate/Cargo.lock
+++ b/substrate/Cargo.lock
@@ -986,7 +986,6 @@ dependencies = [
  "assert_matches 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "error-chain 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "libc 0.2.33 (registry+https://github.com/rust-lang/crates.io-index)",
  "native-runtime 0.1.0",
  "parity-wasm 0.15.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "polkadot-primitives 0.1.0",
@@ -996,6 +995,7 @@ dependencies = [
  "rustc-hex 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.20 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.20 (registry+https://github.com/rust-lang/crates.io-index)",
+ "triehash 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -1235,6 +1235,7 @@ dependencies = [
  "parking_lot 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "polkadot-primitives 0.1.0",
  "polkadot-state-machine 0.1.0",
+ "triehash 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
diff --git a/substrate/executor/Cargo.toml b/substrate/executor/Cargo.toml
index 5329eb7023..41fdef9705 100644
--- a/substrate/executor/Cargo.toml
+++ b/substrate/executor/Cargo.toml
@@ -15,7 +15,7 @@ byteorder = "1.1"
 rustc-hex = "1.0.0"
 native-runtime = { path = "../native-runtime", version = "0.1" }
 runtime-std = { path = "../native-runtime/std", version = "0.1" }
-libc = { version = "0.2.33" }
+triehash = "0.1.0"
 
 [dev-dependencies]
 assert_matches = "1.1"
diff --git a/substrate/executor/src/lib.rs b/substrate/executor/src/lib.rs
index 9935f8aec8..e4ed7f95b0 100644
--- a/substrate/executor/src/lib.rs
+++ b/substrate/executor/src/lib.rs
@@ -36,7 +36,7 @@ extern crate byteorder;
 extern crate rustc_hex;
 extern crate native_runtime;
 extern crate runtime_std;
-extern crate libc;
+extern crate triehash;
 
 #[macro_use]
 extern crate error_chain;
diff --git a/substrate/executor/src/wasm_executor.rs b/substrate/executor/src/wasm_executor.rs
index a741a7b07b..5e18868238 100644
--- a/substrate/executor/src/wasm_executor.rs
+++ b/substrate/executor/src/wasm_executor.rs
@@ -29,6 +29,7 @@ use wasm_utils::{MemoryInstance, UserDefinedElements,
 	AddModuleWithoutFullDependentInstance};
 use primitives::{ed25519, blake2_256, twox_128, twox_256};
 use primitives::hexdisplay::HexDisplay;
+use triehash::ordered_trie_root;
 
 struct Heap {
 	end: u32,
@@ -78,6 +79,17 @@ impl WritePrimitive<u32> for MemoryInstance {
 	}
 }
 
+trait ReadPrimitive<T: Sized> {
+	fn read_primitive(&self, offset: u32) -> ::std::result::Result<T, DummyUserError>;
+}
+
+impl ReadPrimitive<u32> for MemoryInstance {
+	fn read_primitive(&self, offset: u32) -> ::std::result::Result<u32, DummyUserError> {
+		use byteorder::{LittleEndian, ByteOrder};
+		Ok(LittleEndian::read_u32(&self.get(offset, 4).map_err(|_| DummyUserError)?))
+	}
+}
+
 impl_function_executor!(this: FunctionExecutor<'e, E>,
 	ext_print_utf8(utf8_data: *const u8, utf8_len: u32) => {
 		if let Ok(utf8) = this.memory.get(utf8_data, utf8_len as usize) {
@@ -157,6 +169,20 @@ impl_function_executor!(this: FunctionExecutor<'e, E>,
 		let r = this.ext.storage_root();
 		this.memory.set(result, &r[..]).map_err(|_| DummyUserError)?;
 	},
+	ext_enumerated_trie_root(values_data: *const u8, values_len: u32, lens_data: *const u32, lens_len: u32, result: *mut u8) => {
+		let offsets = (0..lens_len)
+			.map(|i| this.memory.read_primitive(lens_data + i * 4))
+			.collect::<::std::result::Result<Vec<u32>, DummyUserError>>()?;
+		let values = offsets.into_iter()
+			.scan(0u32, |acc, v| { let o = *acc; *acc += v; Some((o, v)) })
+			.map(|(offset, len)|
+				this.memory.get(values_data + offset, len as usize)
+					.map_err(|_| DummyUserError)
+			)
+			.collect::<::std::result::Result<Vec<_>, DummyUserError>>()?;
+		let r = ordered_trie_root(values.into_iter());
+		this.memory.set(result, &r[..]).map_err(|_| DummyUserError)?;
+	},
 	ext_chain_id() -> u64 => {
 		this.ext.chain_id()
 	},
@@ -356,6 +382,16 @@ mod tests {
 		);
 	}
 
+	#[test]
+	fn enumerated_trie_root_should_work() {
+		let mut ext = TestExternalities::default();
+		let test_code = include_bytes!("../../wasm-runtime/target/wasm32-unknown-unknown/release/runtime_test.compact.wasm");
+		assert_eq!(
+			WasmExecutor.call(&mut ext, &test_code[..], "test_enumerated_trie_root", &CallData(vec![])).unwrap(),
+			vec![0]
+		);
+	}
+
 	fn tx() -> Vec<u8> { "679fcf0a846b4224c84ecad7d91a26241c46d00cb53d6480a363274e8965ee34b0b80b4b2e3836d3d8f8f12c0c1aef7350af587d9aee3883561d11726068ac0a2f8c6129d816cf51c374bc7f08c3e63ed156cf78aefb4a6550d97b87997977ee00000000000000000228000000d75a980182b10ab7d54bfed3c964073a0ee172f3daa62325af021a68f707511a4500000000000000".convert() }
 
 	#[test]
diff --git a/substrate/native-runtime/std/Cargo.toml b/substrate/native-runtime/std/Cargo.toml
index 0976e4b378..a4f665bfcc 100644
--- a/substrate/native-runtime/std/Cargo.toml
+++ b/substrate/native-runtime/std/Cargo.toml
@@ -12,3 +12,4 @@ parking_lot = "0.5"
 polkadot-state-machine = { path = "../../state_machine" , version = "0.1" }
 environmental = { path = "../../environmental", version = "0.1.0" }
 polkadot-primitives = { path = "../../primitives", version = "0.1.0" }
+triehash = "0.1.0"
diff --git a/substrate/native-runtime/std/src/lib.rs b/substrate/native-runtime/std/src/lib.rs
index be67b81bab..fba5462f7d 100644
--- a/substrate/native-runtime/std/src/lib.rs
+++ b/substrate/native-runtime/std/src/lib.rs
@@ -20,6 +20,7 @@
 extern crate environmental;
 extern crate polkadot_state_machine;
 extern crate polkadot_primitives as primitives;
+extern crate triehash;
 
 use std::fmt;
 use primitives::ed25519;
@@ -99,6 +100,13 @@ pub fn storage_root() -> [u8; 32] {
 	).unwrap_or([0u8; 32])
 }
 
+/// "Commit" all existing operations and get the resultant storage root.
+pub fn enumerated_trie_root(serialised_values: &[&[u8]]) -> [u8; 32] {
+	ext::with(|ext|
+		triehash::ordered_trie_root(serialised_values.iter().map(|s| s.to_vec())).0
+	).unwrap_or([0u8; 32])
+}
+
 /// Conduct a Keccak-256 hash of the given data.
 pub use primitives::{blake2_256, twox_128, twox_256};
 
diff --git a/substrate/wasm-runtime/polkadot/src/lib.rs b/substrate/wasm-runtime/polkadot/src/lib.rs
index 6769ce9146..677272e93f 100644
--- a/substrate/wasm-runtime/polkadot/src/lib.rs
+++ b/substrate/wasm-runtime/polkadot/src/lib.rs
@@ -25,6 +25,7 @@ extern crate runtime_std;
 #[cfg(feature = "with-std")]
 extern crate rustc_hex;
 
+#[cfg(test)]
 #[macro_use]
 extern crate hex_literal;
 
diff --git a/substrate/wasm-runtime/polkadot/src/runtime/system.rs b/substrate/wasm-runtime/polkadot/src/runtime/system.rs
index 54936610e0..8df20f138e 100644
--- a/substrate/wasm-runtime/polkadot/src/runtime/system.rs
+++ b/substrate/wasm-runtime/polkadot/src/runtime/system.rs
@@ -18,8 +18,8 @@
 //! and depositing logs.
 
 use runtime_std::prelude::*;
-use runtime_std::{mem, print, storage_root};
-use codec::KeyedVec;
+use runtime_std::{mem, print, storage_root, enumerated_trie_root};
+use codec::{KeyedVec, Slicable};
 use support::{Hashable, storage, with_env};
 use primitives::{Block, BlockNumber, Hash, UncheckedTransaction, TxOrder};
 use runtime::{staking, session};
@@ -74,9 +74,11 @@ pub mod internal {
 			"Parent hash should be valid."
 		);
 
-		// TODO: check transaction trie root represents the transactions.
-		// this requires non-trivial changes to the externals API or compiling trie rooting into wasm
-		// so will wait until a little later.
+		// check transaction trie root represents the transactions.
+		let txs = block.transactions.iter().map(Slicable::to_vec).collect::<Vec<_>>();
+		let txs_root = enumerated_trie_root(&txs.iter().map(Vec::as_slice).collect::<Vec<_>>());
+//		println!("TR: {}", ::support::HexDisplay::from(&txs_root));
+		assert!(header.transaction_root == txs_root, "Transaction trie root must be valid.");
 
 		// execute transactions
 		block.transactions.iter().for_each(execute_transaction);
@@ -87,7 +89,6 @@ pub mod internal {
 		// any final checks
 		final_checks(&block);
 
-//		println!("SR: {}", ::support::HexDisplay::from(&storage_root()));
 
 		// check storage root.
 		assert!(header.state_root == storage_root(), "Storage root must match that calculated.");
@@ -210,7 +211,7 @@ mod tests {
 			parent_hash: [69u8; 32],
 			number: 1,
 			state_root: hex!("2481853da20b9f4322f34650fea5f240dcbfb266d02db94bfa0153c31f4a29db"),
-			transaction_root: [0u8; 32],		// Unchecked currently.
+			transaction_root: hex!("91fab88ad8c30a6d05ad8e0cf9ab139bf1b8cdddc69abd51cdfa6d2699038af1"),
 			digest: Digest { logs: vec![], },
 		};
 
diff --git a/substrate/wasm-runtime/std/src/lib.rs b/substrate/wasm-runtime/std/src/lib.rs
index 13df07c49f..3feb8c5544 100644
--- a/substrate/wasm-runtime/std/src/lib.rs
+++ b/substrate/wasm-runtime/std/src/lib.rs
@@ -43,6 +43,7 @@ extern "C" {
 	fn ext_get_allocated_storage(key_data: *const u8, key_len: u32, written_out: *mut u32) -> *mut u8;
 	fn ext_get_storage_into(key_data: *const u8, key_len: u32, value_data: *mut u8, value_len: u32, value_offset: u32) -> u32;
 	fn ext_storage_root(result: *mut u8);
+	fn ext_enumerated_trie_root(values_data: *const u8, values_len: u32, lens_data: *const u32, lens_len: u32, result: *mut u8);
 	fn ext_chain_id() -> u64;
 	fn ext_blake2_256(data: *const u8, len: u32, out: *mut u8);
 	fn ext_twox_128(data: *const u8, len: u32, out: *mut u8);
@@ -82,6 +83,21 @@ pub fn storage_root() -> [u8; 32] {
 	result
 }
 
+/// A trie root calculated from enumerated values.
+pub fn enumerated_trie_root(values: &[&[u8]]) -> [u8; 32] {
+	let lens = values.iter().map(|v| (v.len() as u32).to_le()).collect::<Vec<_>>();
+	let values = values.iter().fold(Vec::new(), |mut acc, sl| { acc.extend_from_slice(sl); acc });
+	let mut result: [u8; 32] = Default::default();
+	unsafe {
+		ext_enumerated_trie_root(
+			values.as_ptr(), values.len() as u32,
+			lens.as_ptr(), lens.len() as u32,
+			result.as_mut_ptr()
+		);
+	}
+	result
+}
+
 /// The current relay chain identifier.
 pub fn chain_id() -> u64 {
 	unsafe {
diff --git a/substrate/wasm-runtime/target/wasm32-unknown-unknown/release/runtime_polkadot.compact.wasm b/substrate/wasm-runtime/target/wasm32-unknown-unknown/release/runtime_polkadot.compact.wasm
index efedffaadf..36fe893442 100644
Binary files a/substrate/wasm-runtime/target/wasm32-unknown-unknown/release/runtime_polkadot.compact.wasm and b/substrate/wasm-runtime/target/wasm32-unknown-unknown/release/runtime_polkadot.compact.wasm differ
diff --git a/substrate/wasm-runtime/target/wasm32-unknown-unknown/release/runtime_polkadot.wasm b/substrate/wasm-runtime/target/wasm32-unknown-unknown/release/runtime_polkadot.wasm
index c4e00c3e3e..bd48f63571 100644
Binary files a/substrate/wasm-runtime/target/wasm32-unknown-unknown/release/runtime_polkadot.wasm and b/substrate/wasm-runtime/target/wasm32-unknown-unknown/release/runtime_polkadot.wasm differ