diff --git a/lib/modules/database/index.js b/lib/modules/database/index.js
index 5fc61033..775774ff 100644
--- a/lib/modules/database/index.js
+++ b/lib/modules/database/index.js
@@ -83,7 +83,12 @@ export default class Database extends Base {
    * @param origCB
    * @returns {*}
    */
-  off(refId: number, listeners: Array<DatabaseListener>, remainingListenersCount: number) {
+  off(
+    refId: number,
+    // $FlowFixMe
+    listeners: Array<DatabaseListener>,
+    remainingListenersCount: number
+  ) {
     this.log.debug('off() : ', refId, listeners);
 
     // Delete the reference if there are no more listeners
diff --git a/lib/modules/storage/task.js b/lib/modules/storage/task.js
index d365fceb..3b2ced7d 100644
--- a/lib/modules/storage/task.js
+++ b/lib/modules/storage/task.js
@@ -26,9 +26,13 @@ declare type FuncSnapshotType = null|(snapshot: UploadTaskSnapshotType) => any;
 
 declare type FuncErrorType = null|(error: Error) => any;
 
-declare type NextOrObserverType = null
-  |{ next?: FuncSnapshotType, error?: FuncErrorType, complete?:FuncSnapshotType }
-  |FuncSnapshotType;
+declare type NextOrObserverType = null |
+  {
+    next?: FuncSnapshotType,
+    error?: FuncErrorType,
+    complete?:FuncSnapshotType
+  } |
+  FuncSnapshotType;
 
 /**
  * @url https://firebase.google.com/docs/reference/js/firebase.storage.UploadTask
@@ -93,15 +97,41 @@ export default class StorageTask {
    * @private
    */
   _subscribe(nextOrObserver: NextOrObserverType, error: FuncErrorType, complete: FuncSnapshotType): Function {
-    const observer = isObject(nextOrObserver);
+    let _error;
+    let _next;
+    let _complete;
 
-    const _error = this._interceptErrorEvent(observer ? nextOrObserver.error : error);
-    const _next = this._interceptSnapshotEvent(observer ? nextOrObserver.next : nextOrObserver);
-    const _complete = this._interceptSnapshotEvent(observer ? nextOrObserver.complete : complete);
+    if (typeof nextOrObserver === 'function') {
+      _error = this._interceptErrorEvent(error);
+      _next = this._interceptSnapshotEvent(nextOrObserver);
+      _complete = this._interceptSnapshotEvent(complete);
+    } else if (nextOrObserver) {
+      _error = this._interceptErrorEvent(nextOrObserver.error);
+      _next = this._interceptSnapshotEvent(nextOrObserver.next);
+      _complete = this._interceptSnapshotEvent(nextOrObserver.complete);
+    }
 
-    if (_next) this.storage._addListener(this.path, StorageStatics.TaskEvent.STATE_CHANGED, _next);
-    if (_error) this.storage._addListener(this.path, `${this.type}_failure`, _error);
-    if (_complete) this.storage._addListener(this.path, `${this.type}_success`, _complete);
+    if (_next) {
+      this.storage._addListener(
+        this.path,
+        StorageStatics.TaskEvent.STATE_CHANGED,
+        _next
+      );
+    }
+    if (_error) {
+      this.storage._addListener(
+        this.path,
+        `${this.type}_failure`,
+        _error
+      );
+    }
+    if (_complete) {
+      this.storage._addListener(
+        this.path,
+        `${this.type}_success`,
+        _complete
+      );
+    }
 
     return () => {
       if (_next) this.storage._removeListener(this.path, StorageStatics.TaskEvent.STATE_CHANGED, _next);