diff --git a/modules/libjar/nsJARChannel.cpp b/modules/libjar/nsJARChannel.cpp
index b34db6d1c..dee2863d7 100644
--- a/modules/libjar/nsJARChannel.cpp
+++ b/modules/libjar/nsJARChannel.cpp
@@ -752,7 +752,7 @@ nsJARChannel::GetContentType(nsACString &aResult)
 {
     // If the Jar file has not been open yet,
     // We return application/x-unknown-content-type
-    if (!mOpened && mContentType.IsEmpty()) {
+    if (!mOpened || mContentType.IsEmpty()) {
       aResult.Assign(UNKNOWN_CONTENT_TYPE);
       return NS_OK;
     }