diff --git a/mkdocs.yml b/mkdocs.yml
index a55f053..516f286 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -69,7 +69,7 @@ markdown_extensions:
       custom_fences:
         - name: mermaid
           class: mermaid
-          format: "pymdownx.superfences.fence_code_format"
+          format: !!python/name:pymdownx.superfences.fence_code_format
   - pymdownx.arithmatex:
       generic: true