diff --git a/zipline/pipeline/factors/factor.py b/zipline/pipeline/factors/factor.py
index 4f1751e9..bc05fcb2 100644
--- a/zipline/pipeline/factors/factor.py
+++ b/zipline/pipeline/factors/factor.py
@@ -448,7 +448,7 @@ class CustomFactor(RequiredWindowLengthMixin, CustomTermMixin, Factor):
         describing the data to load and pass to `self.compute`.  If this
         argument is passed to the CustomFactor constructor, we look for a
         class-level attribute named `inputs`.
-    window_length : (optional), int
+    window_length : int, optional
         Number of rows of rows to pass for each input.  If this
         argument is passed to the CustomFactor constructor, we look for a
         class-level attribute named `window_length`.