diff --git a/sbin/mount/getmntopts.c b/sbin/mount/getmntopts.c
index ba35b3e68006..f0026f48cd2b 100644
--- a/sbin/mount/getmntopts.c
+++ b/sbin/mount/getmntopts.c
@@ -36,11 +36,15 @@ static char sccsid[] = "@(#)getmntopts.c	8.3 (Berkeley) 3/29/95";
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
+#include <sys/mount.h>
 #include <sys/stat.h>
 #include <sys/uio.h>
 
+#include <assert.h>
 #include <err.h>
 #include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sysexits.h>
@@ -134,7 +138,8 @@ checkpath(const char *path, char *resolved)
 }
 
 void
-build_iovec(struct iovec **iov, int *iovlen, const char *name, void *val, int len)
+build_iovec(struct iovec **iov, int *iovlen, const char *name, void *val,
+	    size_t len)
 {
 	int i;
 
@@ -150,8 +155,25 @@ build_iovec(struct iovec **iov, int *iovlen, const char *name, void *val, int le
 	(*iov)[i].iov_len = strlen(name) + 1;
 	i++;
 	(*iov)[i].iov_base = val;
-	if (len < 0)
+	if (len == (size_t)-1)
 		len = strlen(val) + 1;
-	(*iov)[i].iov_len = len;
+	(*iov)[i].iov_len = (int)len;
 	*iovlen = ++i;
 }
+
+/*
+ * This function is needed for compatibility with parameters
+ * which used to use the mount_argf() command for the old mount() syscall.
+ */
+void
+build_iovec_argf(struct iovec **iov, int *iovlen, const char *name,
+    const char *fmt, ...)
+{
+	va_list ap;
+	char val[255] = { 0 };
+
+	va_start(ap, fmt);
+	vsnprintf(val, sizeof(val), fmt, ap);  
+	va_end(ap);
+	build_iovec(iov, iovlen, name, strdup(val), (size_t)-1);
+}
diff --git a/sbin/mount/mntopts.h b/sbin/mount/mntopts.h
index 17674da1b600..13a3b532664f 100644
--- a/sbin/mount/mntopts.h
+++ b/sbin/mount/mntopts.h
@@ -95,4 +95,5 @@ void getmntopts(const char *, const struct mntopt *, int *, int *);
 void rmslashes(char *, char *);
 void checkpath(const char *, char resolved_path[]);
 extern int getmnt_silent;
-void build_iovec(struct iovec **iov, int *iovlen, const char *name, void *val, int len);
+void build_iovec(struct iovec **iov, int *iovlen, const char *name, void *val, size_t len);
+void build_iovec_argf(struct iovec **iov, int *iovlen, const char *name, const char *fmt, ...);
diff --git a/sbin/mount/mount_fs.c b/sbin/mount/mount_fs.c
index d56891fcf965..d9b0b3cae307 100644
--- a/sbin/mount/mount_fs.c
+++ b/sbin/mount/mount_fs.c
@@ -104,7 +104,7 @@ mount_fs(const char *vfstype, int argc, char *argv[])
 				*p = '\0';
 				val = p + 1;
 			}
-			build_iovec(&iov, &iovlen, optarg, val, -1);
+			build_iovec(&iov, &iovlen, optarg, val, (size_t)-1);
 			break;
 		case '?':
 		default:
@@ -123,9 +123,9 @@ mount_fs(const char *vfstype, int argc, char *argv[])
 	(void)checkpath(dir, mntpath);
 	(void)rmslashes(dev, dev);
 
-	build_iovec(&iov, &iovlen, "fstype", fstype, -1);
-	build_iovec(&iov, &iovlen, "fspath", mntpath, -1);
-	build_iovec(&iov, &iovlen, "from", dev, -1);
+	build_iovec(&iov, &iovlen, "fstype", fstype, (size_t)-1);
+	build_iovec(&iov, &iovlen, "fspath", mntpath, (size_t)-1);
+	build_iovec(&iov, &iovlen, "from", dev, (size_t)-1);
 	
 	ret = nmount(iov, iovlen, mntflags);
 	if (ret < 0)