diff --git a/state-chain/pallets/cf-vaults/src/lib.rs b/state-chain/pallets/cf-vaults/src/lib.rs
index c8b4f22b0f..6333138a06 100644
--- a/state-chain/pallets/cf-vaults/src/lib.rs
+++ b/state-chain/pallets/cf-vaults/src/lib.rs
@@ -259,8 +259,9 @@ impl<T: Config<I>, I: 'static> VaultKeyWitnessedHandler<T::Chain> for Pallet<T,
 
 impl<T: Config<I>, I: 'static> EpochTransitionHandler for Pallet<T, I> {
 	fn on_expired_epoch(expired_epoch: EpochIndex) {
-		for epoch in
-			VaultStartBlockNumbers::<T, I>::iter_keys().filter(|epoch| *epoch <= expired_epoch)
+		for epoch in VaultStartBlockNumbers::<T, I>::iter_keys()
+			.filter(|epoch| *epoch <= expired_epoch)
+			.collect::<Vec<EpochIndex>>()
 		{
 			VaultStartBlockNumbers::<T, I>::remove(epoch);
 		}