diff --git a/widget/src/windows/nsToolkit.cpp b/widget/src/windows/nsToolkit.cpp
index f178fcada900..97a924919543 100644
--- a/widget/src/windows/nsToolkit.cpp
+++ b/widget/src/windows/nsToolkit.cpp
@@ -288,6 +288,8 @@ BOOL CallOpenSaveFileNameA(LPOPENFILENAMEW aFileNameW, BOOL aOpen)
     ConvertAtoW(ofnA.lpstrFile, MAX_PATH, aFileNameW->lpstrFile);
   }
 
+  aFileNameW->nFilterIndex = ofnA.nFilterIndex;
+
   return rtn;
 }