diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 1f96fed..ab3c4b4 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -14,3 +14,5 @@ python:
   install:
     - method: pip
       path: .
+      extra_requirements:
+        - docs
diff --git a/docs/source/conf.py b/docs/source/conf.py
index 37d222f..694058e 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -10,6 +10,4 @@
 
 exclude_patterns = []
 
-on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
-if not on_rtd:
-    html_theme = 'sphinx_rtd_theme'
+html_theme = 'sphinx_rtd_theme'
diff --git a/pyproject.toml b/pyproject.toml
index e41c065..b408295 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -14,3 +14,8 @@ classifiers = [
   "Topic :: Software Development :: Libraries",
   "Topic :: Text Processing",
 ]
+
+[project.optional-dependencies]
+docs = [
+  "sphinx-rtd-theme",
+]