diff --git a/book/_toc.yml b/book/_toc.yml
index 76584b64aa278e800e3a0707f5b113166ac90470..c4ab36323cf24fe770c3da44d35d0a07f8f79d5f 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -395,7 +395,7 @@ parts:
     - file: programming/week_1_8
       sections:
       - file: external/learn-python/book/08/sympy
-    - file: optimization\gurobi.md
+    - file: optimization/gurobi.md
       title: Gurobi
 
     # THIS IS FOR WEEK 2.5