diff --git a/gio/gio-launch-desktop.c b/gio/gio-launch-desktop.c
index c034f7609..405e8c911 100644
--- a/gio/gio-launch-desktop.c
+++ b/gio/gio-launch-desktop.c
@@ -44,7 +44,7 @@ main (int argc, char *argv[])
     return -1;
 
   r = snprintf (buf, sizeof (buf), "GIO_LAUNCHED_DESKTOP_FILE_PID=%ld", (long) pid);
-  if (r >= sizeof (buf))
+  if (r < 0 || (size_t) r >= sizeof (buf))
     return -1;
 
   putenv (buf);