--- orig/lisp/spam.el
+++ mod/lisp/spam.el
@@ -2679,7 +2679,7 @@
 	  (apply 'call-process-region
 		 (point-min) (point-max)
 		 spam-sa-learn-path
-		 nil nil nil "--mbox"
+		 nil 0 nil "--mbox"
 		 (if spam-sa-learn-rebuild
 		     (list action)
 		   `("--no-rebuild" ,action)))))))