diff --git a/sys/vm/vm_zone.c b/sys/vm/vm_zone.c
index 5c6431b9cd0a..79e3fbad4da2 100644
--- a/sys/vm/vm_zone.c
+++ b/sys/vm/vm_zone.c
@@ -451,8 +451,7 @@ sysctl_vm_zone(SYSCTL_HANDLER_ARGS)
 		offset += len;
 	}
 	mtx_unlock(&zone_mtx);
-	offset--;
-	*offset = '\0';
+	*offset++ = '\0';
 	error = SYSCTL_OUT(req, tmpbuf, offset - tmpbuf);
 out:
 	FREE(tmpbuf, M_TEMP);