diff --git a/sphinx_automodapi/automodsumm.py b/sphinx_automodapi/automodsumm.py
index 8fb5602..e9dc2d7 100644
--- a/sphinx_automodapi/automodsumm.py
+++ b/sphinx_automodapi/automodsumm.py
@@ -261,7 +261,7 @@ def patched_generate_dot(self, name, urls={}, env=None,
     # Make a new mapping dictionary that uses class full names by importing each
     # class documented name
     fullname_urls = {self.class_name(try_import(name), 0, None): url
-                     for name, url in urls.items()}
+                     for name, url in urls.items() if try_import(name) is not None}
     return old_generate_dot(self, name, urls=fullname_urls, env=env,
                             graph_attrs=graph_attrs, node_attrs=node_attrs,
                             edge_attrs=edge_attrs)