diff --git a/mrbgems/mruby-io/README.md b/mrbgems/mruby-io/README.md
index 6e0a8cc84..3629cdb5c 100644
--- a/mrbgems/mruby-io/README.md
+++ b/mrbgems/mruby-io/README.md
@@ -164,7 +164,7 @@ Add the line below to your build configuration.
 | File#ctime                  |          |          |
 | File#flock                  | o        |          |
 | File#lstat                  |          |          |
-| File#mtime                  |          |          |
+| File#mtime                  | o        |          |
 | File#path                   | o        |          |
 | File#size                   |          |          |
 | File#truncate               |          |          |