Index: sys/kern/kern_descrip.c
===================================================================
--- sys/kern/kern_descrip.c
+++ sys/kern/kern_descrip.c
@@ -780,7 +780,9 @@
 		}
 		if (arg >= 0) {
 			bsize = fp->f_vnode->v_mount->mnt_stat.f_iosize;
-			fp->f_seqcount = (arg + bsize - 1) / bsize;
+			arg = MIN(arg, INT_MAX - bsize + 1);
+			fp->f_seqcount = MIN(IO_SEQMAX,
+				(arg + bsize - 1) / bsize);
 			atomic_set_int(&fp->f_flag, FRDAHEAD);
 		} else {
 			atomic_clear_int(&fp->f_flag, FRDAHEAD);
Index: sys/sys/file.h
===================================================================
--- sys/sys/file.h
+++ sys/sys/file.h
@@ -179,7 +179,7 @@
 	/*
 	 *  DTYPE_VNODE specific fields.
 	 */
-	int		f_seqcount;	/* (a) Count of sequential accesses. */
+	short		f_seqcount;	/* (a) Count of sequential accesses. */
 	off_t		f_nextoff;	/* next expected read/write offset. */
 	union {
 		struct cdev_privdata *fvn_cdevpriv;