diff --git a/src/mux_h2.c b/src/mux_h2.c
index c06d5d6..5bb8518 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -2177,7 +2177,7 @@
 		goto strm_err;
 	}
 
-	if ((h2s->flags & H2_SF_DATA_CLEN) && h2c->dfl > h2s->body_len) {
+	if ((h2s->flags & H2_SF_DATA_CLEN) && (h2c->dfl - h2c->dpl) > h2s->body_len) {
 		/* RFC7540#8.1.2 */
 		error = H2_ERR_PROTOCOL_ERROR;
 		goto strm_err;