diff --git a/util/src/hashdb.rs b/util/src/hashdb.rs
index 8217413ef..ca4120702 100644
--- a/util/src/hashdb.rs
+++ b/util/src/hashdb.rs
@@ -86,7 +86,7 @@ pub trait HashDB: AsHashDB + Send + Sync {
 	fn emplace(&mut self, key: H256, value: DBValue);
 
 	/// Remove a datum previously inserted. Insertions can be "owed" such that the same number of `insert()`s may
-	/// happen without the data being eventually being inserted into the DB.
+	/// happen without the data being eventually being inserted into the DB. It can be "owed" more than once.
 	///
 	/// # Examples
 	/// ```rust
@@ -100,6 +100,10 @@ pub trait HashDB: AsHashDB + Send + Sync {
 	///   let key = &d.sha3();
 	///   m.remove(key);	// OK - we now owe an insertion.
 	///   assert!(!m.contains(key));
+	///   m.remove(key);	// OK - we now owe two insertions.
+	///   assert!(!m.contains(key));
+	///   m.insert(d);	// OK - still owed.
+	///   assert!(!m.contains(key));
 	///   m.insert(d);	// OK - now it's "empty" again.
 	///   assert!(!m.contains(key));
 	///   m.insert(d);	// OK - now we've
diff --git a/util/src/memorydb.rs b/util/src/memorydb.rs
index bd96347ab..cc8d0a3de 100644
--- a/util/src/memorydb.rs
+++ b/util/src/memorydb.rs
@@ -246,46 +246,57 @@ impl HashDB for MemoryDB {
 	}
 }
 
-#[test]
-fn memorydb_remove_and_purge() {
-	let hello_bytes = b"Hello world!";
-	let hello_key = hello_bytes.sha3();
+#[cfg(test)]
+mod tests {
+	use super::*;
 
-	let mut m = MemoryDB::new();
-	m.remove(&hello_key);
-	assert_eq!(m.raw(&hello_key).unwrap().1, -1);
-	m.purge();
-	assert_eq!(m.raw(&hello_key).unwrap().1, -1);
-	m.insert(hello_bytes);
-	assert_eq!(m.raw(&hello_key).unwrap().1, 0);
-	m.purge();
-	assert_eq!(m.raw(&hello_key), None);
+	#[test]
+	fn memorydb_remove_and_purge() {
+		let hello_bytes = b"Hello world!";
+		let hello_key = hello_bytes.sha3();
 
-	let mut m = MemoryDB::new();
-	assert!(m.remove_and_purge(&hello_key).is_none());
-	assert_eq!(m.raw(&hello_key).unwrap().1, -1);
-	m.insert(hello_bytes);
-	m.insert(hello_bytes);
-	assert_eq!(m.raw(&hello_key).unwrap().1, 1);
-	assert_eq!(&*m.remove_and_purge(&hello_key).unwrap(), hello_bytes);
-	assert_eq!(m.raw(&hello_key), None);
-	assert!(m.remove_and_purge(&hello_key).is_none());
-}
-
-#[test]
-fn consolidate() {
-	let mut main = MemoryDB::new();
-	let mut other = MemoryDB::new();
-	let remove_key = other.insert(b"doggo");
-	main.remove(&remove_key);
-
-	let insert_key = other.insert(b"arf");
-	main.emplace(insert_key, DBValue::from_slice(b"arf"));
-
-	main.consolidate(other);
-
-	let overlay = main.drain();
-
-	assert_eq!(overlay.get(&remove_key).unwrap(), &(DBValue::from_slice(b"doggo"), 0));
-	assert_eq!(overlay.get(&insert_key).unwrap(), &(DBValue::from_slice(b"arf"), 2));
+		let mut m = MemoryDB::new();
+		m.remove(&hello_key);
+		assert_eq!(m.raw(&hello_key).unwrap().1, -1);
+		m.purge();
+		assert_eq!(m.raw(&hello_key).unwrap().1, -1);
+		m.insert(hello_bytes);
+		assert_eq!(m.raw(&hello_key).unwrap().1, 0);
+		m.purge();
+		assert_eq!(m.raw(&hello_key), None);
+
+		let mut m = MemoryDB::new();
+		assert!(m.remove_and_purge(&hello_key).is_none());
+		assert_eq!(m.raw(&hello_key).unwrap().1, -1);
+		m.insert(hello_bytes);
+		m.insert(hello_bytes);
+		assert_eq!(m.raw(&hello_key).unwrap().1, 1);
+		assert_eq!(&*m.remove_and_purge(&hello_key).unwrap(), hello_bytes);
+		assert_eq!(m.raw(&hello_key), None);
+		assert!(m.remove_and_purge(&hello_key).is_none());
+	}
+
+	#[test]
+	fn consolidate() {
+		let mut main = MemoryDB::new();
+		let mut other = MemoryDB::new();
+		let remove_key = other.insert(b"doggo");
+		main.remove(&remove_key);
+
+		let insert_key = other.insert(b"arf");
+		main.emplace(insert_key, DBValue::from_slice(b"arf"));
+
+		let negative_remove_key = other.insert(b"negative");
+		other.remove(&negative_remove_key);	// ref cnt: 0
+		other.remove(&negative_remove_key);	// ref cnt: -1
+		main.remove(&negative_remove_key);	// ref cnt: -1
+
+		main.consolidate(other);
+
+		let overlay = main.drain();
+
+		assert_eq!(overlay.get(&remove_key).unwrap(), &(DBValue::from_slice(b"doggo"), 0));
+		assert_eq!(overlay.get(&insert_key).unwrap(), &(DBValue::from_slice(b"arf"), 2));
+		assert_eq!(overlay.get(&negative_remove_key).unwrap(), &(DBValue::from_slice(b"negative"), -2));
+	}
 }