diff --git a/lib/libc/gen/exterr_cat_filenames.h b/lib/libc/gen/exterr_cat_filenames.h
--- a/lib/libc/gen/exterr_cat_filenames.h
+++ b/lib/libc/gen/exterr_cat_filenames.h
@@ -2,6 +2,7 @@
  * Automatically @generated, use
  * tools/build/make_libc_exterr_cat_filenames.sh
  */
+	[EXTERR_CAT_VMM] = "dev/vmm/vmm_dev.c",
 	[EXTERR_CAT_FUSE_DEVICE] = "fs/fuse/fuse_device.c",
 	[EXTERR_CAT_FUSE_VFS] = "fs/fuse/fuse_vfsops.c",
 	[EXTERR_CAT_FUSE_VNOPS] = "fs/fuse/fuse_vnops.c",
diff --git a/sys/dev/vmm/vmm_dev.c b/sys/dev/vmm/vmm_dev.c
--- a/sys/dev/vmm/vmm_dev.c
+++ b/sys/dev/vmm/vmm_dev.c
@@ -8,6 +8,8 @@
 
 #include <sys/param.h>
 #include <sys/conf.h>
+#define	EXTERR_CATEGORY	EXTERR_CAT_VMM
+#include <sys/exterrvar.h>
 #include <sys/fcntl.h>
 #include <sys/ioccom.h>
 #include <sys/jail.h>
@@ -1008,7 +1010,8 @@
 	if ((flags & VMMCTL_CREATE_DESTROY_ON_CLOSE) == 0 &&
 	    (error = priv_check_cred(cred, PRIV_VMM_CREATE)) != 0) {
 		sx_xunlock(&vmmdev_mtx);
-		return (error);
+		return (EXTERROR(error,
+		    "An unprivileged user must run VMs in monitor mode"));
 	}
 
 	error = vm_create(name, &vm);
diff --git a/sys/sys/exterr_cat.h b/sys/sys/exterr_cat.h
--- a/sys/sys/exterr_cat.h
+++ b/sys/sys/exterr_cat.h
@@ -37,6 +37,7 @@
 #define	EXTERR_CAT_GEOM		12
 #define	EXTERR_CAT_FUSE_VFS	13
 #define	EXTERR_CAT_FUSE_DEVICE	14
+#define	EXTERR_CAT_VMM		15
 
 #endif