diff --git a/lib/output.c b/lib/output.c
index 2d8c3694..90d0030f 100644
--- a/lib/output.c
+++ b/lib/output.c
@@ -223,7 +223,7 @@ lws_issue_raw_ext_access(struct libwebsocket *wsi,
 			 * Keep amount spilled small to minimize chance of this
 			 */
 			if (n != eff_buf.token_len) {
-				lwsl_err("Unable to spill ext %d vs %s\n",
+				lwsl_err("Unable to spill ext %d vs %d\n",
 							  eff_buf.token_len, n);
 				return -1;
 			}