--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -9725,16 +9725,17 @@ PresShell::Observe(nsISupports* aSubject
     if (!AssumeAllFramesVisible() && mPresContext->IsRootContentDocument()) {
       DoUpdateApproximateFrameVisibility(/* aRemoveOnly = */ true);
     }
     return NS_OK;
   }
 
   if (!nsCRT::strcmp(aTopic, NS_WIDGET_WAKE_OBSERVER_TOPIC)) {
     mLastOSWake = TimeStamp::Now();
+    return NS_OK;
   }
 
   NS_WARNING("unrecognized topic in PresShell::Observe");
   return NS_ERROR_FAILURE;
 }
 
 bool
 nsIPresShell::AddRefreshObserverInternal(nsARefreshObserver* aObserver,