diff --git a/sphinx_d2lang/__init__.py b/sphinx_d2lang/__init__.py
index 10784fe..a942297 100644
--- a/sphinx_d2lang/__init__.py
+++ b/sphinx_d2lang/__init__.py
@@ -4,9 +4,14 @@ from .d2lang import D2langDirective
 
 from typing import Any, Dict, List, Tuple
 
+from shutil import whitch
+
 def setup(application: Sphinx) -> Dict[str, Any]:
     """
     setup extension.
     """
-    application.add_directive('d2lang', D2langDirective)
-    return {"version": '0.0.1', "parallel_read_safe": True}
+    if which('d2'):
+        application.add_directive('d2lang', D2langDirective)
+        return {"version": '0.0.1', "parallel_read_safe": True}
+    else:
+        raise