diff --git a/readthedocs/doc_builder/python_environments.py b/readthedocs/doc_builder/python_environments.py
index d77adabb58b..02a1c97d667 100644
--- a/readthedocs/doc_builder/python_environments.py
+++ b/readthedocs/doc_builder/python_environments.py
@@ -226,7 +226,7 @@ def install_core_requirements(self):
             pip_requirements.append('mkdocs')
         else:
             pip_requirements.append('readthedocs-sphinx-ext')
-            requirements.extend(['sphinx', 'sphinx-rtd-theme'])
+            requirements.extend(['sphinx', 'sphinx_rtd_theme'])
 
         cmd = [
             'conda',