--- infix.system.orig
+++ infix.system
@@ -2,7 +2,7 @@
 
 (mk:defsystem infix
   :source-pathname "cl-library:infix;"
-  :source-extension "cl"
+  :source-extension "lisp"
   :binary-pathname nil
   :binary-extension nil
   :components ((:file "infix")))