diff --git a/src/tools.c b/src/tools.c
index db17fda..e543fd6 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -943,6 +943,8 @@
 		ss.ss_family = AF_UNSPEC;
 
 	if (ss.ss_family == AF_CUST_SOCKPAIR) {
+		struct sockaddr_storage ss2;
+		socklen_t addr_len;
 		char *endptr;
 
 		new_fd = strtol(str2, &endptr, 10);
@@ -951,6 +953,13 @@
 			goto out;
 		}
 
+		/* just verify that it's a socket */
+		addr_len = sizeof(ss2);
+		if (getsockname(new_fd, (struct sockaddr *)&ss2, &addr_len) == -1) {
+			memprintf(err, "cannot use file descriptor '%d' : %s.\n", new_fd, strerror(errno));
+			goto out;
+		}
+
 		((struct sockaddr_in *)&ss)->sin_addr.s_addr = new_fd;
 		((struct sockaddr_in *)&ss)->sin_port = 0;
 	}