diff --git a/src/mux_h1.c b/src/mux_h1.c
index 4594a62..78145df 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -984,7 +984,7 @@
 		/* Incomplete or invalid message. If the buffer is full, it's an
 		 * error because headers are too large to be handled by the
 		 * parser. */
-		if (ret < 0 || (!ret && b_full(buf)))
+		if (ret < 0 || (!ret && !buf_room_for_htx_data(buf)))
 			goto error;
 		goto end;
 	}