--- a/dom/workers/ServiceWorkerPeriodicUpdater.cpp
+++ b/dom/workers/ServiceWorkerPeriodicUpdater.cpp
@@ -55,17 +55,17 @@ ServiceWorkerPeriodicUpdater::Observe(ns
                                       const char16_t* aData)
 {
   // In tests, the pref is set to false so that the idle-daily service does not
   // trigger updates leading to intermittent failures.
   // We're called from SpecialPowers inside tests, in which case we need to
   // update during the test run, for which we use a non-empty aData.
   NS_NAMED_LITERAL_STRING(CallerSpecialPowers, "Caller:SpecialPowers");
   if (strcmp(aTopic, OBSERVER_TOPIC_IDLE_DAILY) == 0 &&
-      (sPeriodicUpdatesEnabled || CallerSpecialPowers.Equals(aData))) {
+      (sPeriodicUpdatesEnabled || (aData && CallerSpecialPowers.Equals(aData)))) {
     // First, update all registrations in the parent process.
     nsCOMPtr<nsIServiceWorkerManager> swm =
       mozilla::services::GetServiceWorkerManager();
     if (swm) {
         swm->UpdateAllRegistrations();
     }
 
     // Now, tell all child processes to update their registrations as well.