diff --git a/lib/pure/os.nim b/lib/pure/os.nim
index 434fc3a26e..13c6d6113a 100644
--- a/lib/pure/os.nim
+++ b/lib/pure/os.nim
@@ -638,14 +638,14 @@ proc getAppFilename*(): string {.rtl, extern: "nos$1", tags: [ReadIOEffect], noW
   # /proc/<pid>/path/a.out (complete pathname)
   when defined(windows):
     var bufsize = int32(MAX_PATH)
-    var buf = newWideCString("", bufsize)
+    var buf = newWideCString(bufsize)
     while true:
       var L = getModuleFileNameW(0, buf, bufsize)
       if L == 0'i32:
         result = "" # error!
         break
       elif L > bufsize:
-        buf = newWideCString("", L)
+        buf = newWideCString(L)
         bufsize = L
       else:
         result = buf$L