diff --git a/netwerk/base/nsIOService.cpp b/netwerk/base/nsIOService.cpp
index 1843add5436..1d45d43e694 100644
--- a/netwerk/base/nsIOService.cpp
+++ b/netwerk/base/nsIOService.cpp
@@ -1400,6 +1400,7 @@ nsIOService::Observe(nsISupports *subject,
 
         if (mCaptivePortalService) {
             static_cast<CaptivePortalService*>(mCaptivePortalService.get())->Stop();
+            mCaptivePortalService = nullptr;
         }
 
         // Break circular reference.