diff --git a/parser/htmlparser/src/nsParser.cpp b/parser/htmlparser/src/nsParser.cpp
index 78722c01e68d..42acdb4d033c 100644
--- a/parser/htmlparser/src/nsParser.cpp
+++ b/parser/htmlparser/src/nsParser.cpp
@@ -2568,6 +2568,9 @@ nsresult nsParser::OnDataAvailable(nsIRequest *request, nsISupports* aContext,
       rv = ResumeParse();
     }
   }
+  else {
+    rv = NS_ERROR_UNEXPECTED;
+  }
 
   return rv;
 }