diff -Naur ruby-shadow-2.1.3.orig/shadow.c ruby-shadow-2.1.3/shadow.c
--- ruby-shadow-2.1.3.orig/shadow.c	2012-04-17 15:07:29.489334366 +0900
+++ ruby-shadow-2.1.3/shadow.c	2012-04-17 15:14:40.955219365 +0900
@@ -209,7 +209,7 @@
 {
   int result;
 
-  if( rb_iterator_p() ){
+  if( rb_block_given_p() ){
     result = lckpwdf();
     if( result == -1 ){
       rb_raise(rb_eFileLock,"password file was locked");