diff --git a/src/serve.c b/src/serve.c
index c7ec0b7..cd4b0c0 100644
--- a/src/serve.c
+++ b/src/serve.c
@@ -512,10 +512,13 @@ int server_accept( struct server * params )
 	union mysockaddr client_address;
 	fd_set           fds;
 	socklen_t        socklen=sizeof(client_address);
+	/* We select on this fd to receive OS signals (only a few of
+	 * which we're interested in, see flexnbd.c */
+	int              signal_fd = flexnbd_signal_fd( params->flexnbd );
 
 	FD_ZERO(&fds);
 	FD_SET(params->server_fd, &fds);
-	FD_SET(flexnbd_signal_fd( params->flexnbd ), &fds);
+	if( 0 <  signal_fd ) { FD_SET(signal_fd, &fds); }
 	self_pipe_fd_set( params->close_signal, &fds );
 	self_pipe_fd_set( params->acl_updated_signal, &fds );
 
@@ -527,7 +530,7 @@ int server_accept( struct server * params )
 		return 0;
 	}
 
-	if ( FD_ISSET( flexnbd_signal_fd( params->flexnbd ), &fds ) ){
+	if ( 0 < signal_fd && FD_ISSET( signal_fd, &fds ) ){
 		debug( "Stop signal received." );
 		server_close_clients( params );
 		return 0;
diff --git a/tests/check_serve.c b/tests/check_serve.c
index e58073d..18a8325 100644
--- a/tests/check_serve.c
+++ b/tests/check_serve.c
@@ -145,6 +145,7 @@ START_TEST( test_acl_update_closes_bad_client )
 	 * a client socket.
 	 */
 	struct flexnbd flexnbd;
+	flexnbd.signal_fd = -1;
 	struct server * s = server_create( &flexnbd, "127.0.0.7", "0", dummy_file, 0, 0, NULL, 1, 1 );
 	struct acl * new_acl = acl_create( 0, NULL, 1 );
 	struct client * c;