diff --git a/ethcore/src/account.rs b/ethcore/src/account.rs
index aa5a0c4bd..c36c35232 100644
--- a/ethcore/src/account.rs
+++ b/ethcore/src/account.rs
@@ -183,11 +183,11 @@ impl Account {
 	#[cfg(test)]
 	/// Determine whether there are any un-`commit()`-ed storage-setting operations.
 	pub fn storage_is_clean(&self) -> bool { self.storage_overlay.borrow().iter().find(|&(_, &(f, _))| f == Filth::Dirty).is_none() }
-	
+
 	#[cfg(test)]
 	/// return the storage root associated with this account or None if it has been altered via the overlay.
 	pub fn storage_root(&self) -> Option<&H256> { if self.storage_is_clean() {Some(&self.storage_root)} else {None} }
-	
+
 	/// return the storage overlay.
 	pub fn storage_overlay(&self) -> Ref<HashMap<H256, (Filth, H256)>> { self.storage_overlay.borrow() }
 
@@ -198,7 +198,11 @@ impl Account {
 	pub fn add_balance(&mut self, x: &U256) { self.balance = self.balance + *x; }
 
 	/// Increment the nonce of the account by one.
-	pub fn sub_balance(&mut self, x: &U256) { self.balance = self.balance - *x; }
+	/// Panics if balance is less than `x`
+	pub fn sub_balance(&mut self, x: &U256) {
+		assert!(self.balance >= *x);
+		self.balance = self.balance - *x;
+	}
 
 	/// Commit the `storage_overlay` to the backing DB and update `storage_root`.
 	pub fn commit_storage(&mut self, db: &mut AccountDBMut) {
diff --git a/ethcore/src/externalities.rs b/ethcore/src/externalities.rs
index b5a0c2539..20c0222d2 100644
--- a/ethcore/src/externalities.rs
+++ b/ethcore/src/externalities.rs
@@ -355,6 +355,7 @@ mod tests {
 	}
 
 	#[test]
+	#[should_panic]
 	fn can_call_fail_empty() {
 		let mut setup = TestSetup::new();
 		let state = setup.state.reference_mut();