diff --git a/product/PortalTransforms/libtransforms/commandtransform.py b/product/PortalTransforms/libtransforms/commandtransform.py
index 374be60936918196349734c19fd3f0a9de14a96c..cc4692df69788b3179252b9fb96b1c9ea1b51cd2 100644
--- a/product/PortalTransforms/libtransforms/commandtransform.py
+++ b/product/PortalTransforms/libtransforms/commandtransform.py
@@ -166,5 +166,5 @@ class subprocesstransform:
             return cache
 
         finally:
-            if isinstance(stdin_file, file):
+            if hasattr(stdin_file, 'close'):
                 stdin_file.close()