diff --git a/osdep/subprocess-win.c b/osdep/subprocess-win.c
index de33768d22..c08cacc6ba 100644
--- a/osdep/subprocess-win.c
+++ b/osdep/subprocess-win.c
@@ -211,6 +211,7 @@ static wchar_t *convert_environ(void *ctx, char **env)
             abort();
         pos += count;
     }
+    ret[pos] = L'\0';
 
     return ret;
 }