diff --git a/include/types/connection.h b/include/types/connection.h
index 827df36..889decb 100644
--- a/include/types/connection.h
+++ b/include/types/connection.h
@@ -425,7 +425,8 @@
 	PROTO_MODE_NONE = 0,
 	PROTO_MODE_TCP  = 1 << 0, // must not be changed!
 	PROTO_MODE_HTTP = 1 << 1, // must not be changed!
-	PROTO_MODE_ANY  = PROTO_MODE_TCP | PROTO_MODE_HTTP,
+	PROTO_MODE_HTX  = 1 << 2, // must not be changed!
+	PROTO_MODE_ANY  = PROTO_MODE_TCP | PROTO_MODE_HTTP, // note: HTX is experimental and must not appear here
 };
 
 enum proto_proxy_side {
diff --git a/include/types/proxy.h b/include/types/proxy.h
index b5f5b9b..da09848 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -151,7 +151,7 @@
 #define PR_O2_SRC_ADDR	0x00100000	/* get the source ip and port for logs */
 
 #define PR_O2_FAKE_KA   0x00200000      /* pretend we do keep-alive with server eventhough we close */
-/* unused: 0x00400000 */
+#define PR_O2_USE_HTX   0x00400000      /* use the HTX representation for the HTTP protocol */
 #define PR_O2_EXP_NONE  0x00000000      /* http-check : no expect rule */
 #define PR_O2_EXP_STS   0x00800000      /* http-check expect status */
 #define PR_O2_EXP_RSTS  0x01000000      /* http-check expect rstatus */