diff --git a/distutils/compilers/C/base.py b/distutils/compilers/C/base.py
index 4767b7f3..d4641018 100644
--- a/distutils/compilers/C/base.py
+++ b/distutils/compilers/C/base.py
@@ -236,8 +236,11 @@ def _check_macro_definition(self, defn):
     def _is_valid_macro(name, value=None):
         """
         A valid macro is a ``name : str`` and a ``value : str | None``.
+
+        >>> Compiler._is_valid_macro('foo', None)
+        True
         """
-        return isinstance(name, str) and isinstance(value, (str, None))
+        return isinstance(name, str) and isinstance(value, (str, type(None)))
 
     # -- Bookkeeping methods -------------------------------------------