diff --git a/django/core/meta/__init__.py b/django/core/meta/__init__.py
index 0c6078705a..f934f9dd6c 100644
--- a/django/core/meta/__init__.py
+++ b/django/core/meta/__init__.py
@@ -563,7 +563,8 @@ class ModelBase(type):
         new_class = type.__new__(cls, name, bases, attrs)
 
         # Give the class a docstring -- its definition.
-        new_class.__doc__ = "%s.%s(%s)" % (opts.module_name, name, ", ".join([f.name for f in opts.fields]))
+        if new_class.__doc__ is None:
+            new_class.__doc__ = "%s.%s(%s)" % (opts.module_name, name, ", ".join([f.name for f in opts.fields]))
 
         # Create the standard, module-level API helper functions such
         # as get_object() and get_list().