diff --git a/readthedocs/doc_builder/python_environments.py b/readthedocs/doc_builder/python_environments.py
index 5abe1209833..beecb562ea1 100644
--- a/readthedocs/doc_builder/python_environments.py
+++ b/readthedocs/doc_builder/python_environments.py
@@ -615,7 +615,8 @@ def _append_core_requirements(self):
 
             for item in dependencies:
                 if isinstance(item, dict) and 'pip' in item:
-                    pip_requirements.extend(item.get('pip', []))
+                    # NOTE: pip can be ``None``
+                    pip_requirements.extend(item.get('pip') or [])
                     dependencies.remove(item)
                     break