diff --git a/netwerk/base/nsFileStreams.cpp b/netwerk/base/nsFileStreams.cpp
index ac259c1c7e94..6be501456656 100644
--- a/netwerk/base/nsFileStreams.cpp
+++ b/netwerk/base/nsFileStreams.cpp
@@ -378,6 +378,9 @@ nsFileStreamBase::DoPendingOpen()
 
     case eOpened:
         MOZ_ASSERT(mFD);
+        if (NS_WARN_IF(!mFD)) {
+          return NS_ERROR_FAILURE;
+        }
         return NS_OK;
 
     case eClosed: