diff --git a/src/proto_http.c b/src/proto_http.c
index 3cb8bd014..da0a8a83f 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -360,6 +360,32 @@ const char http_is_ver_token[256] = {
 };
 
 
+/*
+ * Silent debug that outputs only in strace, using fd #-1. Trash is modified.
+ */
+#if defined(DEBUG_FSM)
+static void http_silent_debug(int line, struct session *s)
+{
+	int size = 0;
+	size += snprintf(trash + size, sizeof(trash) - size,
+			 "[%04d] req: p=%d(%d) s=%d bf=%08x an=%08x data=%p size=%d l=%d w=%p r=%p lr=%p sm=%d fw=%ld tf=%08x\n",
+			 line,
+			 s->si[0].state, s->si[0].fd, s->txn.req.msg_state, s->req->flags, s->req->analysers,
+			 s->req->data, s->req->size, s->req->l, s->req->w, s->req->r, s->req->lr, s->req->send_max, s->req->to_forward, s->txn.flags);
+	write(-1, trash, size);
+	size = 0;
+	size += snprintf(trash + size, sizeof(trash) - size,
+			 " %04d  rep: p=%d(%d) s=%d bf=%08x an=%08x data=%p size=%d l=%d w=%p r=%p lr=%p sm=%d fw=%ld\n",
+			 line,
+			 s->si[1].state, s->si[1].fd, s->txn.rsp.msg_state, s->rep->flags, s->rep->analysers,
+			 s->rep->data, s->rep->size, s->rep->l, s->rep->w, s->rep->r, s->rep->lr, s->rep->send_max, s->rep->to_forward);
+
+	write(-1, trash, size);
+}
+#else
+#define http_silent_debug(l,s)  do { } while (0)
+#endif
+
 /*
  * Adds a header and its CRLF at the tail of buffer <b>, just before the last
  * CRLF. Text length is measured first, so it cannot be NULL.