diff --git a/Process.yml b/Process.yml
index ec1d1ba..cf8e36d 100644
--- a/Process.yml
+++ b/Process.yml
@@ -47,6 +47,8 @@ $graph:
   symbols:
     - cwl:File
     - cwl:Directory
+    - cwl:stdout
+    - cwl:stderr
   doc:
     - "Extends primitive types with the concept of a file and directory as a builtin type."
     - "File: A File object"