diff --git a/browser/components/loop/MozLoopService.jsm b/browser/components/loop/MozLoopService.jsm
index 1655acaac3d..9783f8dda2a 100644
--- a/browser/components/loop/MozLoopService.jsm
+++ b/browser/components/loop/MozLoopService.jsm
@@ -259,7 +259,9 @@ let MozLoopServiceInternal = {
     }
 
     // We need to register, so save the callback.
-    this.registrationCallbacks.push(callback);
+    if (callback) {
+      this.registrationCallbacks.push(callback);
+    }
 
     // If we're already in progress, just return straight away.
     if (this.registrationInProgress) {