diff --git a/IPython/utils/py3compat.py b/IPython/utils/py3compat.py
index 4f0ed41..f42f55c 100644
--- a/IPython/utils/py3compat.py
+++ b/IPython/utils/py3compat.py
@@ -47,7 +47,9 @@ def _modify_str_or_docstring(str_change_func):
             func = func_or_str
             doc = func.__doc__
         
-        doc = str_change_func(doc)
+        # PYTHONOPTIMIZE=2 strips docstrings, so they can disappear unexpectedly
+        if doc is not None:
+            doc = str_change_func(doc)
         
         if func:
             func.__doc__ = doc