diff --git a/src/debug.h b/src/debug.h
index 7b823ee1..37d58e95 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -180,7 +180,7 @@ static inline gpgme_ssize_t
 _trace_sysres_ssize_t (gpgme_ssize_t res, int lvl, const char *func, int line)
 {
   if (res >= 0)
-    _gpgme_debug (NULL, lvl, 3, func, NULL, NULL, "result=%zd", res);
+    _gpgme_debug (NULL, lvl, 3, func, NULL, NULL, "result=%zd", (ssize_t)res);
   else
     _gpgme_debug (NULL, lvl, -1, NULL, NULL, NULL,
                   "%s:%d: error: %s (%d)\n",