diff --git a/lib/win_util.cpp b/lib/win_util.cpp
index cb213c06ab..394940bd15 100644
--- a/lib/win_util.cpp
+++ b/lib/win_util.cpp
@@ -911,6 +911,8 @@ char* windows_format_error_string(
         if (lpszTemp) {
             LocalFree((HLOCAL) lpszTemp);
         }
+    } else {
+        strcpy(pszBuf, "(unknown error)");
     }
 
     return pszBuf;