diff --git a/setup.py b/setup.py
index e03876a..f5ec2ac 100644
--- a/setup.py
+++ b/setup.py
@@ -461,7 +461,7 @@ if parser.has_option('build_ext', 'mx_include_dir'):
     mxincludedir = parser.get('build_ext', 'mx_include_dir')
 else:
     mxincludedir = os.path.join(get_python_inc(plat_specific=1), "mx")
-if os.path.exists(mxincludedir):
+if not use_pydatetime and os.path.exists(mxincludedir):
     # Build the support for mx: we will check at runtime if it can be imported
     include_dirs.append(mxincludedir)
     define_macros.append(('HAVE_MXDATETIME', '1'))