diff --git a/lib/modules/database/reference.js b/lib/modules/database/reference.js
index 6fb43b1b..0055ae59 100644
--- a/lib/modules/database/reference.js
+++ b/lib/modules/database/reference.js
@@ -157,11 +157,7 @@ export default class Reference extends ReferenceBase {
    * @param onComplete
    * @param applyLocally
    */
-  transaction(
-    transactionUpdate: Function,
-    onComplete?: (?Error, any, ?Snapshot) => any,
-    applyLocally: boolean = false
-  ) {
+  transaction(transactionUpdate: Function, onComplete, applyLocally: boolean = false) {
     if (!isFunction(transactionUpdate)) return Promise.reject(new Error('Missing transactionUpdate function argument.'));
 
     return new Promise((resolve, reject) => {