--- a/netwerk/base/nsIOService.cpp
+++ b/netwerk/base/nsIOService.cpp
@@ -1796,16 +1796,18 @@ nsIOService::SpeculativeConnectInternal(
     // reward is slim with tcp peers closely located to the browser.
     nsresult rv;
     nsCOMPtr<nsIProtocolProxyService> pps =
             do_GetService(NS_PROTOCOLPROXYSERVICE_CONTRACTID, &rv);
     NS_ENSURE_SUCCESS(rv, rv);
 
     nsCOMPtr<nsIPrincipal> loadingPrincipal = aPrincipal;
 
+    NS_ASSERTION(aPrincipal, "We expect passing a principal here.");
+
     // If the principal is given, we use this prinicpal directly. Otherwise,
     // we fallback to use the system principal.
     if (!aPrincipal) {
         nsCOMPtr<nsIScriptSecurityManager> secMan(
             do_GetService(NS_SCRIPTSECURITYMANAGER_CONTRACTID, &rv));
         NS_ENSURE_SUCCESS(rv, rv);
         rv = secMan->GetSystemPrincipal(getter_AddRefs(loadingPrincipal));
         NS_ENSURE_SUCCESS(rv, rv);