diff --git a/sys/kern/kern_memio.c b/sys/kern/kern_memio.c
--- a/sys/kern/kern_memio.c
+++ b/sys/kern/kern_memio.c
@@ -222,7 +222,7 @@
 mmrw(cdev_t dev, struct uio *uio, int flags)
 {
 	int o;
-	u_int c;
+	size_t		c;
 	u_int poolsize;
 	u_long v;
 	struct iovec *iov;