Typo fix

Closes #7520.

PiperOrigin-RevId: 235573006

site/docs/backward-compatibility.md

diff --git a/site/docs/backward-compatibility.md b/site/docs/backward-compatibility.md
index 487618f..9485787 100644
--- a/site/docs/backward-compatibility.md
+++ b/site/docs/backward-compatibility.md
@@ -61,7 +61,7 @@
 1. After the code is migrated, the users can check whether they migrated
    successfully by building with `--incompatible_foo=true`. However, their
    code will continue to work in the same release in default state (where
-   `--incompatible_foo` is of), as well after the migration window is over
+   `--incompatible_foo` is off), as well after the migration window is over
    (at which point the flag will be effectively on).
 
 ## Communicating incompatible changes