diff --git a/doc/source/conf.py b/doc/source/conf.py
index 3ac5fe478..a038e8e3c 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -23,10 +23,11 @@ from custom_directives import CustomGalleryItemDirective
 # These lines added to enable Sphinx to work without installing Ray.
 import mock
 MOCK_MODULES = [
-    "blist", "gym", "gym.spaces", "ray._raylet", "ray.core.generated",
-    "ray.core.generated.gcs_pb2", "ray.core.generated.ray.protocol.Task",
-    "scipy", "scipy.signal", "scipy.stats", "tensorflow_probability",
-    "tensorflow", "tensorflow.contrib", "tensorflow.contrib.all_reduce",
+    "blist", "gym", "gym.spaces", "psutil", "ray._raylet",
+    "ray.core.generated", "ray.core.generated.gcs_pb2",
+    "ray.core.generated.ray.protocol.Task", "scipy", "scipy.signal",
+    "scipy.stats", "tensorflow_probability", "tensorflow",
+    "tensorflow.contrib", "tensorflow.contrib.all_reduce",
     "tensorflow.contrib.all_reduce.python", "tensorflow.contrib.layers",
     "tensorflow.contrib.rnn", "tensorflow.contrib.slim", "tensorflow.core",
     "tensorflow.core.util", "tensorflow.python", "tensorflow.python.client",