diff --git a/polkadot/runtime/src/runtime/governance.rs b/polkadot/runtime/src/runtime/governance.rs
index 9138a3eddf..80620d578f 100644
--- a/polkadot/runtime/src/runtime/governance.rs
+++ b/polkadot/runtime/src/runtime/governance.rs
@@ -189,7 +189,7 @@ mod tests {
 			assert!(!session::validators().into_iter().position(|v| &v == &one).is_none());
 
 			// Block 1: Make proposal. Approve it. Era length changes.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			public::propose(&one, &Proposal::StakingSetSessionsPerEra(2));
 			public::approve(&two, 1);
 			staking::internal::check_new_era();
@@ -212,13 +212,13 @@ mod tests {
 			assert!(!session::validators().into_iter().position(|v| &v == &one).is_none());
 
 			// Block 1: Make proposal. Fail it.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			public::propose(&one, &Proposal::StakingSetSessionsPerEra(2));
 			staking::internal::check_new_era();
 			assert_eq!(staking::era_length(), 1);
 
 			// Block 2: Make proposal. Approve it. It should change era length.
-			with_env(|e| e.block_number = 2);
+			system::testing::set_block_number(2);
 			public::propose(&one, &Proposal::StakingSetSessionsPerEra(2));
 			public::approve(&two, 2);
 			staking::internal::check_new_era();
@@ -241,7 +241,7 @@ mod tests {
 			assert!(!session::validators().into_iter().position(|v| &v == &one).is_none());
 
 			// Block 1: Make proposal. Will have only 1 vote. No change.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			public::propose(&one, &Proposal::StakingSetSessionsPerEra(2));
 			staking::internal::check_new_era();
 			assert_eq!(staking::era_length(), 1);
@@ -264,7 +264,7 @@ mod tests {
 			assert!(!session::validators().into_iter().position(|v| &v == &one).is_none());
 
 			// Block 1: Make proposal. Will have only 1 vote. No change.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			public::propose(&one, &Proposal::StakingSetSessionsPerEra(2));
 			public::approve(&two, 0);
 			staking::internal::check_new_era();
@@ -288,7 +288,7 @@ mod tests {
 			assert!(!session::validators().into_iter().position(|v| &v == &one).is_none());
 
 			// Block 1: Make proposal. Will have only 1 vote. No change.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			public::propose(&one, &Proposal::StakingSetSessionsPerEra(2));
 			public::approve(&two, 1);
 			public::approve(&two, 1);
@@ -313,7 +313,7 @@ mod tests {
 			assert!(!session::validators().into_iter().position(|v| &v == &one).is_none());
 
 			// Block 1: Make proposal. Will have only 1 vote. No change.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			public::propose(&one, &Proposal::StakingSetSessionsPerEra(2));
 			public::propose(&two, &Proposal::StakingSetSessionsPerEra(2));
 			staking::internal::check_new_era();
@@ -337,7 +337,7 @@ mod tests {
 			assert!(!session::validators().into_iter().position(|v| &v == &one).is_none());
 
 			// Block 1: Make proposal. Will have only 1 vote. No change.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			public::approve(&two, 1);
 			staking::internal::check_new_era();
 			assert_eq!(staking::era_length(), 1);
@@ -361,7 +361,7 @@ mod tests {
 			assert!(!session::validators().into_iter().position(|v| &v == &one).is_none());
 
 			// Block 1: Make proposal. Will have only 1 vote. No change.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			public::propose(&one, &Proposal::StakingSetSessionsPerEra(2));
 			public::approve(&four, 1);
 			staking::internal::check_new_era();
diff --git a/polkadot/runtime/src/runtime/session.rs b/polkadot/runtime/src/runtime/session.rs
index 01a5f78bbc..4eb5bf5055 100644
--- a/polkadot/runtime/src/runtime/session.rs
+++ b/polkadot/runtime/src/runtime/session.rs
@@ -217,46 +217,46 @@ mod tests {
 		let mut t = simple_setup();
 		with_externalities(&mut t, || {
 			// Block 1: Change to length 3; no visible change.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			set_length(3);
 			check_rotate_session();
 			assert_eq!(length(), 2);
 			assert_eq!(current_index(), 0);
 
 			// Block 2: Length now changed to 3. Index incremented.
-			with_env(|e| e.block_number = 2);
+			system::testing::set_block_number(2);
 			set_length(3);
 			check_rotate_session();
 			assert_eq!(length(), 3);
 			assert_eq!(current_index(), 1);
 
 			// Block 3: Length now changed to 3. Index incremented.
-			with_env(|e| e.block_number = 3);
+			system::testing::set_block_number(3);
 			check_rotate_session();
 			assert_eq!(length(), 3);
 			assert_eq!(current_index(), 1);
 
 			// Block 4: Change to length 2; no visible change.
-			with_env(|e| e.block_number = 4);
+			system::testing::set_block_number(4);
 			set_length(2);
 			check_rotate_session();
 			assert_eq!(length(), 3);
 			assert_eq!(current_index(), 1);
 
 			// Block 5: Length now changed to 2. Index incremented.
-			with_env(|e| e.block_number = 5);
+			system::testing::set_block_number(5);
 			check_rotate_session();
 			assert_eq!(length(), 2);
 			assert_eq!(current_index(), 2);
 
 			// Block 6: No change.
-			with_env(|e| e.block_number = 6);
+			system::testing::set_block_number(6);
 			check_rotate_session();
 			assert_eq!(length(), 2);
 			assert_eq!(current_index(), 2);
 
 			// Block 7: Next index.
-			with_env(|e| e.block_number = 7);
+			system::testing::set_block_number(7);
 			check_rotate_session();
 			assert_eq!(length(), 2);
 			assert_eq!(current_index(), 3);
@@ -268,17 +268,17 @@ mod tests {
 		let mut t = simple_setup();
 		with_externalities(&mut t, || {
 			// Block 1: No change
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			check_rotate_session();
 			assert_eq!(consensus::authorities(), vec![[11u8; 32], [21u8; 32]]);
 
 			// Block 2: Session rollover, but no change.
-			with_env(|e| e.block_number = 2);
+			system::testing::set_block_number(2);
 			check_rotate_session();
 			assert_eq!(consensus::authorities(), vec![[11u8; 32], [21u8; 32]]);
 
 			// Block 3: Set new key for validator 2; no visible change.
-			with_env(|e| e.block_number = 3);
+			system::testing::set_block_number(3);
 			set_key(&[20; 32], &[22; 32]);
 			assert_eq!(consensus::authorities(), vec![[11u8; 32], [21u8; 32]]);
 
@@ -286,7 +286,7 @@ mod tests {
 			assert_eq!(consensus::authorities(), vec![[11u8; 32], [21u8; 32]]);
 
 			// Block 4: Session rollover, authority 2 changes.
-			with_env(|e| e.block_number = 4);
+			system::testing::set_block_number(4);
 			check_rotate_session();
 			assert_eq!(consensus::authorities(), vec![[11u8; 32], [22u8; 32]]);
 		});
diff --git a/polkadot/runtime/src/runtime/staking.rs b/polkadot/runtime/src/runtime/staking.rs
index cca0a92718..7ed94b9202 100644
--- a/polkadot/runtime/src/runtime/staking.rs
+++ b/polkadot/runtime/src/runtime/staking.rs
@@ -310,7 +310,7 @@ mod tests {
 			assert_eq!(session::validators(), vec![[10u8; 32], [20u8; 32]]);
 
 			// Block 1: Add three validators. No obvious change.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			stake(&one);
 			stake(&two);
 			stake(&four);
@@ -318,39 +318,39 @@ mod tests {
 			assert_eq!(session::validators(), vec![[10u8; 32], [20u8; 32]]);
 
 			// Block 2: New validator set now.
-			with_env(|e| e.block_number = 2);
+			system::testing::set_block_number(2);
 			check_new_era();
 			assert_eq!(session::validators(), vec![four.clone(), two.clone()]);
 
 			// Block 3: Unstake highest, introduce another staker. No change yet.
-			with_env(|e| e.block_number = 3);
+			system::testing::set_block_number(3);
 			stake(&three);
 			unstake(&four);
 			check_new_era();
 
 			// Block 4: New era - validators change.
-			with_env(|e| e.block_number = 4);
+			system::testing::set_block_number(4);
 			check_new_era();
 			assert_eq!(session::validators(), vec![three.clone(), two.clone()]);
 
 			// Block 5: Transfer stake from highest to lowest. No change yet.
-			with_env(|e| e.block_number = 5);
+			system::testing::set_block_number(5);
 			transfer(&four, &one, 40);
 			check_new_era();
 
 			// Block 6: Lowest now validator.
-			with_env(|e| e.block_number = 6);
+			system::testing::set_block_number(6);
 			check_new_era();
 			assert_eq!(session::validators(), vec![one.clone(), three.clone()]);
 
 			// Block 7: Unstake three. No change yet.
-			with_env(|e| e.block_number = 7);
+			system::testing::set_block_number(7);
 			unstake(&three);
 			check_new_era();
 			assert_eq!(session::validators(), vec![one.clone(), three.clone()]);
 
 			// Block 8: Back to one and two.
-			with_env(|e| e.block_number = 8);
+			system::testing::set_block_number(8);
 			check_new_era();
 			assert_eq!(session::validators(), vec![one.clone(), two.clone()]);
 		});
@@ -369,21 +369,21 @@ mod tests {
 			assert_eq!(current_era(), 0u64);
 
 			// Block 1: No change.
-			with_env(|e| e.block_number = 1);
+			system::testing::set_block_number(1);
 			check_new_era();
 			assert_eq!(sessions_per_era(), 2u64);
 			assert_eq!(last_era_length_change(), 0u64);
 			assert_eq!(current_era(), 0u64);
 
 			// Block 2: Simple era change.
-			with_env(|e| e.block_number = 2);
+			system::testing::set_block_number(2);
 			check_new_era();
 			assert_eq!(sessions_per_era(), 2u64);
 			assert_eq!(last_era_length_change(), 0u64);
 			assert_eq!(current_era(), 1u64);
 
 			// Block 3: Schedule an era length change; no visible changes.
-			with_env(|e| e.block_number = 3);
+			system::testing::set_block_number(3);
 			set_sessions_per_era(3);
 			check_new_era();
 			assert_eq!(sessions_per_era(), 2u64);
@@ -391,28 +391,28 @@ mod tests {
 			assert_eq!(current_era(), 1u64);
 
 			// Block 4: Era change kicks in.
-			with_env(|e| e.block_number = 4);
+			system::testing::set_block_number(4);
 			check_new_era();
 			assert_eq!(sessions_per_era(), 3u64);
 			assert_eq!(last_era_length_change(), 4u64);
 			assert_eq!(current_era(), 2u64);
 
 			// Block 5: No change.
-			with_env(|e| e.block_number = 5);
+			system::testing::set_block_number(5);
 			check_new_era();
 			assert_eq!(sessions_per_era(), 3u64);
 			assert_eq!(last_era_length_change(), 4u64);
 			assert_eq!(current_era(), 2u64);
 
 			// Block 6: No change.
-			with_env(|e| e.block_number = 6);
+			system::testing::set_block_number(6);
 			check_new_era();
 			assert_eq!(sessions_per_era(), 3u64);
 			assert_eq!(last_era_length_change(), 4u64);
 			assert_eq!(current_era(), 2u64);
 
 			// Block 7: Era increment.
-			with_env(|e| e.block_number = 7);
+			system::testing::set_block_number(7);
 			check_new_era();
 			assert_eq!(sessions_per_era(), 3u64);
 			assert_eq!(last_era_length_change(), 4u64);
diff --git a/polkadot/runtime/src/runtime/system.rs b/polkadot/runtime/src/runtime/system.rs
index c7972c949a..935f801924 100644
--- a/polkadot/runtime/src/runtime/system.rs
+++ b/polkadot/runtime/src/runtime/system.rs
@@ -264,6 +264,15 @@ fn info_expect_equal_hash(given: &Hash, expected: &Hash) {
 	}
 }
 
+#[cfg(any(feature = "std", test))]
+pub mod testing {
+	use super::*;
+
+	pub fn set_block_number(n: BlockNumber) {
+		with_env(|e| e.block_number = n);
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;
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 7072339a07..3b3fb8f78c 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 57be086703..cb08a3c72b 100644
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