diff --git a/gdbstub/syscalls.c b/gdbstub/syscalls.c
index e855df21ab..d8bb90cc1c 100644
--- a/gdbstub/syscalls.c
+++ b/gdbstub/syscalls.c
@@ -127,7 +127,7 @@ void gdb_do_syscall(gdb_syscall_complete_cb cb, const char *fmt, ...)
             case 's':
                 i64 = va_arg(va, uint64_t);
                 i32 = va_arg(va, uint32_t);
-                p += snprintf(p, p_end - p, "%" PRIx64 "/%x" PRIx32, i64, i32);
+                p += snprintf(p, p_end - p, "%" PRIx64 "/%" PRIx32, i64, i32);
                 break;
             default:
             bad_format: