diff --git a/md_mermaid.py b/md_mermaid.py
index 69bfea4..9a37604 100644
--- a/md_mermaid.py
+++ b/md_mermaid.py
@@ -85,7 +85,7 @@ def run(self, lines):
 class MermaidExtension(Extension):
     """ Add source code hilighting to markdown codeblocks. """
 
-    def extendMarkdown(self, md, md_globals):
+    def extendMarkdown(self, md):
         """ Add HilitePostprocessor to Markdown instance. """
         # Insert a preprocessor before ReferencePreprocessor
         md.preprocessors.register(MermaidPreprocessor(md), 'mermaid', 35)