diff --git a/usr.sbin/autofs/automount.c b/usr.sbin/autofs/automount.c
--- a/usr.sbin/autofs/automount.c
+++ b/usr.sbin/autofs/automount.c
@@ -80,6 +80,8 @@
 	free(fsid_str);
 	if (error != 0)
 		log_warn("cannot unmount %s", sb->f_mntonname);
+	else
+		rpc_umntall();
 
 	return (error);
 }
diff --git a/usr.sbin/autofs/autounmountd.c b/usr.sbin/autofs/autounmountd.c
--- a/usr.sbin/autofs/autounmountd.c
+++ b/usr.sbin/autofs/autounmountd.c
@@ -170,7 +170,8 @@
 			log_warn("cannot unmount %s (%s)",
 			    mountpoint, fsid_str);
 		}
-	}
+	} else
+		rpc_umntall();
 
 	free(fsid_str);
 
diff --git a/usr.sbin/autofs/common.h b/usr.sbin/autofs/common.h
--- a/usr.sbin/autofs/common.h
+++ b/usr.sbin/autofs/common.h
@@ -96,6 +96,7 @@
 void	defined_init(void);
 void	defined_parse_and_add(char *def);
 void	lesser_daemon(void);
+void	rpc_umntall(void);
 
 int	main_automount(int argc, char **argv);
 int	main_automountd(int argc, char **argv);
diff --git a/usr.sbin/autofs/common.c b/usr.sbin/autofs/common.c
--- a/usr.sbin/autofs/common.c
+++ b/usr.sbin/autofs/common.c
@@ -1204,6 +1204,19 @@
 	}
 }
 
+/*
+ * Applicable to NFSv3 only, see rpc.umntall(8).
+ */
+void
+rpc_umntall(void)
+{
+	FILE *f;
+
+	f = auto_popen("rpc.umntall", "-k", NULL);
+	assert(f != NULL);
+	auto_pclose(f);
+}
+
 int
 main(int argc, char **argv)
 {