diff --git a/book/_toc.yml b/book/_toc.yml
index 91a0b9f..373feb7 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -20,7 +20,7 @@ parts:
       sections:
       - file: syntax_exercises/007.md
       - file: syntax_exercises/008.md
-      - file: syntax_exercises/009.md
+      - file: syntax_exercises\009.md
     - file: references.md
     - file: changelog.md
     - file: credits.md