diff --git a/storage/mozStorageConnection.cpp b/storage/mozStorageConnection.cpp
index 7d6895736f26..c4c3be68e7dd 100644
--- a/storage/mozStorageConnection.cpp
+++ b/storage/mozStorageConnection.cpp
@@ -847,7 +847,7 @@ nsresult Connection::databaseElementExists(
   return convertResultCode(srv);
 }
 
-bool Connection::findFunctionByInstance(nsISupports* aInstance) {
+bool Connection::findFunctionByInstance(mozIStorageFunction* aInstance) {
   sharedDBMutex.assertCurrentThreadOwns();
 
   for (auto iter = mFunctions.Iter(); !iter.Done(); iter.Next()) {
@@ -1545,9 +1545,7 @@ nsresult Connection::initializeClone(Connection* aClone, bool aReadOnly) {
     const nsACString& key = iter.Key();
     Connection::FunctionInfo data = iter.UserData();
 
-    mozIStorageFunction* function =
-        static_cast<mozIStorageFunction*>(data.function.get());
-    rv = aClone->CreateFunction(key, data.numArgs, function);
+    rv = aClone->CreateFunction(key, data.numArgs, data.function);
     if (NS_FAILED(rv)) {
       NS_WARNING("Failed to copy function to cloned connection");
     }
diff --git a/storage/mozStorageConnection.h b/storage/mozStorageConnection.h
index 9f4db99a89c4..837a9c9bde9c 100644
--- a/storage/mozStorageConnection.h
+++ b/storage/mozStorageConnection.h
@@ -55,7 +55,7 @@ class Connection final : public mozIStorageConnection,
    * Structure used to describe user functions on the database connection.
    */
   struct FunctionInfo {
-    nsCOMPtr<nsISupports> function;
+    nsCOMPtr<mozIStorageFunction> function;
     int32_t numArgs;
   };
 
@@ -350,7 +350,7 @@ class Connection final : public mozIStorageConnection,
   nsresult databaseElementExists(enum DatabaseElementType aElementType,
                                  const nsACString& aElementName, bool* _exists);
 
-  bool findFunctionByInstance(nsISupports* aInstance);
+  bool findFunctionByInstance(mozIStorageFunction* aInstance);
 
   static int sProgressHelper(void* aArg);
   // Generic progress handler