--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -2215,17 +2215,17 @@ SelectProfile(nsIProfileLock* *aResult, 
                                       getter_AddRefs(profile));
     if (NS_SUCCEEDED(rv)) {
       if (gDoProfileReset) {
         NS_WARNING("Profile reset is only supported for the default profile.");
         gDoProfileReset = false;
       }
 
       nsCOMPtr<nsIProfileUnlocker> unlocker;
-      rv = profile->Lock(nullptr, aResult);
+      rv = profile->Lock(getter_AddRefs(unlocker), aResult);
       if (NS_SUCCEEDED(rv)) {
         if (aProfileName)
           aProfileName->Assign(nsDependentCString(arg));
         return NS_OK;
       }
 
       return ProfileLockedDialog(profile, unlocker, aNative, aResult);
     }