diff --git a/sys/gdb/gdb_main.c b/sys/gdb/gdb_main.c
index a7e53c67fb9..68b1e3317cc 100644
--- a/sys/gdb/gdb_main.c
+++ b/sys/gdb/gdb_main.c
@@ -418,7 +418,7 @@ do_qXfer_threads_read(void)
 	 */
 	if (offset != 0) {
 		if (offset != ctx.qXfer.last_offset) {
-			printf("%s: Resumed offset %ju != expected %ju\n",
+			printf("%s: Resumed offset %ju != expected %zu\n",
 			    __func__, offset, ctx.qXfer.last_offset);
 			error = ESPIPE;
 			goto request_error;