diff --git a/setup.py b/setup.py
index b27d7a5..41547f2 100755
--- a/setup.py
+++ b/setup.py
@@ -67,7 +67,7 @@ def read(*names, **kwargs):
 class BinaryDistribution(Distribution):
     """Distribution which almost always forces a binary package with platform name"""
     def has_ext_modules(self):
-        return super().has_ext_modules() or os.environ.get('SETUPPY_ALLOW_PURE')
+        return super().has_ext_modules() or not os.environ.get('SETUPPY_ALLOW_PURE')
 
 
 setup(