diff --git a/CHANGES.md b/CHANGES.md
index fab8f653..ed3b208d 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -5,6 +5,8 @@
   missing version query functions.
   https://github.com/joblib/threadpoolctl/pull/88
 
+- Fixed an attribute error when python is run with -OO.
+  https://github.com/joblib/threadpoolctl/pull/87
 
 2.2.0 (2021-07-09)
 ==================
diff --git a/threadpoolctl.py b/threadpoolctl.py
index 94db2989..d32d6697 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -98,7 +98,8 @@ class _dl_phdr_info(ctypes.Structure):
 
 def _format_docstring(*args, **kwargs):
     def decorator(o):
-        o.__doc__ = o.__doc__.format(*args, **kwargs)
+        if o.__doc__ is not None:
+            o.__doc__ = o.__doc__.format(*args, **kwargs)
         return o
 
     return decorator