diff --git a/include/proto/connection.h b/include/proto/connection.h
index 397c478..8921a06 100644
--- a/include/proto/connection.h
+++ b/include/proto/connection.h
@@ -152,6 +152,7 @@
 	if (conn_ctrl_ready(conn))
 		fd_delete(conn->t.sock.fd);
 
+	conn->t.sock.fd = DEAD_FD_MAGIC;
 	conn->flags &= ~(CO_FL_XPRT_READY|CO_FL_CTRL_READY);
 }
 
@@ -481,7 +482,7 @@
 	conn->data = NULL;
 	conn->owner = NULL;
 	conn->send_proxy_ofs = 0;
-	conn->t.sock.fd = -1; /* just to help with debugging */
+	conn->t.sock.fd = DEAD_FD_MAGIC;
 	conn->err_code = CO_ER_NONE;
 	conn->target = NULL;
 	conn->proxy_netns = NULL;
diff --git a/include/types/fd.h b/include/types/fd.h
index 8299a02..7f63093 100644
--- a/include/types/fd.h
+++ b/include/types/fd.h
@@ -76,6 +76,19 @@
 	FD_ST_READY
 };
 
+
+/* This is the value used to mark a file descriptor as dead. This value is
+ * negative, this is important so that tests on fd < 0 properly match. It
+ * also has the nice property of being highly negative but not overflowing
+ * nor changing sign on 32-bit machines when multipled by sizeof(fdtab).
+ * This ensures that any unexpected dereference of such an uninitialized
+ * file descriptor will lead to so large a dereference that it will crash
+ * the process at the exact location of the bug with a clean stack trace
+ * instead of causing silent manipulation of other FDs. And it's readable
+ * when found in a dump.
+ */
+#define DEAD_FD_MAGIC 0xFDDEADFD
+
 /* info about one given fd */
 struct fdtab {
 	void (*iocb)(int fd);                /* I/O handler */