diff --git a/reg-tests/connection/tcp_to_http_upgrade.vtc b/reg-tests/connection/tcp_to_http_upgrade.vtc
index 093ba48e1..48ebebaef 100644
--- a/reg-tests/connection/tcp_to_http_upgrade.vtc
+++ b/reg-tests/connection/tcp_to_http_upgrade.vtc
@@ -155,6 +155,13 @@ client c_err3 -connect ${h1_err3h1_sock} {
     expect_close
 } -run
 
+# TCP > HTTP upgrade with a parsing error
+client c_err4 -connect ${h1_fe2h1_sock} {
+    send "GET / BAD-VERSION\r\n\r\n"
+    rxresp
+    expect resp.status == 400
+} -run
+
 # To be sure no other request was received by the server
 client c_end -connect ${s1_sock} {
     txreq
diff --git a/src/mux_h1.c b/src/mux_h1.c
index a8421b76c..c511cfede 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -2629,7 +2629,8 @@ static int h1_send_error(struct h1c *h1c)
 		}
 	}
 
-	if (h1c->h1s) {
+	if (h1c->state == H1_CS_EMBRYONIC) {
+		BUG_ON(h1c->h1s == NULL || h1s_sc(h1c->h1s) == NULL);
 		TRACE_DEVEL("Abort embryonic H1S", H1_EV_H1C_ERR, h1c->conn, h1c->h1s);
 		h1s_destroy(h1c->h1s);
 	}