diff --git a/doc/configuration.txt b/doc/configuration.txt
index 9fb099937..aa6baabb4 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -5338,13 +5338,14 @@ external-check command <command>
 
   The arguments passed to the to the command are:
 
-  proxy_address proxy_port server_address server_port
+  <proxy_address> <proxy_port> <server_address> <server_port>
 
-  The proxy_address and proxy_port are derived from the first listener
-  that is either IPv4, IPv6 or a UNIX socket. It is an error for no such
-  listeners to exist. In the case of a UNIX socket listener the
-  proxy_address will be the path of the socket and the proxy_port will
-  be the string "NOT_USED".
+  The <proxy_address> and <proxy_port> are derived from the first listener
+  that is either IPv4, IPv6 or a UNIX socket. In the case of a UNIX socket
+  listener the proxy_address will be the path of the socket and the
+  <proxy_port> will be the string "NOT_USED". In a backend section, it's not
+  possible to determine a listener, and both <proxy_address> and <proxy_port>
+  will have the string value "NOT_USED".
 
   If the command executed and exits with a zero status then the check is
   considered to have passed, otherwise the check is considered to have
diff --git a/src/checks.c b/src/checks.c
index 5dc95b2a2..bb8b719eb 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -1589,11 +1589,6 @@ static int prepare_external_check(struct check *check)
 			break;
 		}
 
-	if (!listener) {
-		err_fmt = "Starting [%s:%s] check: no listener.\n";
-		goto err;
-	}
-
 	check->curpid = NULL;
 
 	check->envp = calloc(2, sizeof(check->argv));
@@ -1612,19 +1607,25 @@ static int prepare_external_check(struct check *check)
 
 	check->argv[0] = px->check_command;
 
-	if (listener->addr.ss_family == AF_INET ||
+	if (!listener) {
+		check->argv[1] = strdup("NOT_USED");
+		check->argv[2] = strdup("NOT_USED");
+	}
+	else if (listener->addr.ss_family == AF_INET ||
 	    listener->addr.ss_family == AF_INET6) {
 		addr_to_str(&listener->addr, host, sizeof(host));
 		check->argv[1] = strdup(host);
 		port_to_str(&listener->addr, serv, sizeof(serv));
 		check->argv[2] = strdup(serv);
-	} else if (listener->addr.ss_family == AF_UNIX) {
+	}
+	else if (listener->addr.ss_family == AF_UNIX) {
 		const struct sockaddr_un *un;
 
 		un = (struct sockaddr_un *)&listener->addr;
 		check->argv[1] = strdup(un->sun_path);
 		check->argv[2] = strdup("NOT_USED");
-	} else {
+	}
+	else {
 		goto err;
 	}