Index: libexec/rc/rc.d/automount
===================================================================
--- libexec/rc/rc.d/automount
+++ libexec/rc/rc.d/automount
@@ -18,8 +18,15 @@
 
 automount_start()
 {
+	local master_flags=""
+	for master in ${autofs_masters}; do
+		case ${master} in
+		/*) master_flags="${master_flags} -m ${master}" ;;
+		*) master_flags="${master_flags} -m /etc/autofs/master_${master}" ;;
+		esac
+	done
 
-	/usr/sbin/automount ${automount_flags}
+	/usr/sbin/automount ${automount_flags} ${master_flags}
 }
 
 automount_stop()
Index: usr.sbin/autofs/automount.c
===================================================================
--- usr.sbin/autofs/automount.c
+++ usr.sbin/autofs/automount.c
@@ -313,7 +313,7 @@
 usage_automount(void)
 {
 
-	fprintf(stderr, "usage: automount [-D name=value][-o opts][-Lcfuv]\n");
+	fprintf(stderr, "usage: automount [-D name=value][-m master][-o opts][-Lcfuv]\n");
 	exit(1);
 }
 
@@ -324,6 +324,8 @@
 	int ch, debug = 0, show_maps = 0;
 	char *options = NULL;
 	bool do_unmount = false, force_unmount = false, flush = false;
+	const char **masters;
+	size_t nmasters;
 
 	/*
 	 * Note that in automount(8), the only purpose of variable
@@ -331,7 +333,13 @@
 	 */
 	defined_init();
 
-	while ((ch = getopt(argc, argv, "D:Lfco:uv")) != -1) {
+	/* Allocate an array for at most argc master files + NULL. */
+	if ((masters = malloc((argc + 1) * sizeof(char *))) == NULL)
+		log_err(1, "malloc");
+	masters[0] = AUTO_MASTER_PATH;
+	nmasters = 1;
+
+	while ((ch = getopt(argc, argv, "D:Lfcm:o:uv")) != -1) {
 		switch (ch) {
 		case 'D':
 			defined_parse_and_add(optarg);
@@ -345,6 +353,9 @@
 		case 'f':
 			force_unmount = true;
 			break;
+		case 'm':
+			masters[nmasters++] = optarg;
+			break;
 		case 'o':
 			options = concat(options, ',', optarg);
 			break;
@@ -363,6 +374,9 @@
 	if (argc != 0)
 		usage_automount();
 
+	/* Terminate list of masters. */
+	masters[nmasters] = NULL;
+
 	if (force_unmount && !do_unmount)
 		usage_automount();
 
@@ -379,7 +393,7 @@
 	}
 
 	root = node_new_root();
-	parse_master(root, AUTO_MASTER_PATH);
+	parse_master(root, masters);
 
 	if (show_maps) {
 		if (show_maps > 1) {
Index: usr.sbin/autofs/common.h
===================================================================
--- usr.sbin/autofs/common.h
+++ usr.sbin/autofs/common.h
@@ -90,7 +90,7 @@
 int	node_expand_defined(struct node *root);
 void	node_expand_indirect_maps(struct node *n);
 void	node_print(const struct node *n, const char *cmdline_options);
-void	parse_master(struct node *root, const char *path);
+void	parse_master(struct node *root, const char **paths);
 void	parse_map(struct node *parent, const char *map, const char *args,
 	    bool *wildcards);
 char	*defined_expand(const char *string);
Index: usr.sbin/autofs/common.c
===================================================================
--- usr.sbin/autofs/common.c
+++ usr.sbin/autofs/common.c
@@ -1154,22 +1154,27 @@
 }
 
 void
-parse_master(struct node *root, const char *master)
+parse_master(struct node *root, const char **masters)
 {
+	const char * master;
 
-	log_debugx("parsing auto_master file at \"%s\"", master);
+	while (*masters) {
+		master = *masters++;
 
-	yyin = fopen(master, "r");
-	if (yyin == NULL)
-		err(1, "unable to open %s", master);
+		log_debugx("parsing auto_master file at \"%s\"", master);
 
-	parse_master_yyin(root, master);
+		yyin = fopen(master, "r");
+		if (yyin == NULL)
+			err(1, "unable to open %s", master);
 
-	fclose(yyin);
-	yyin = NULL;
+		parse_master_yyin(root, master);
 
-	log_debugx("done parsing \"%s\"", master);
+		fclose(yyin);
+		yyin = NULL;
 
+		log_debugx("done parsing \"%s\"", master);
+	}
+
 	node_expand_includes(root, true);
 	node_expand_direct_maps(root);
 }