diff --git a/monitor/nlmon.c b/monitor/nlmon.c
index 77f5dda4..087b374f 100644
--- a/monitor/nlmon.c
+++ b/monitor/nlmon.c
@@ -6876,7 +6876,7 @@ static bool nlmon_receive(struct l_io *io, void *user_data)
 	unsigned char buf[8192];
 	unsigned char control[32];
 	ssize_t bytes_read;
-	size_t nlmsg_len;
+	int nlmsg_len;
 	int fd;
 
 	fd = l_io_get_fd(io);