Index: enumerator.c
===================================================================
--- enumerator.c	(revision 36594)
+++ enumerator.c	(working copy)
@@ -105,7 +105,7 @@
 VALUE rb_cEnumerator;
 VALUE rb_cLazy;
 static ID id_rewind, id_each, id_new, id_initialize, id_yield, id_call;
-static ID id_eqq, id_next, id_result, id_lazy, id_receiver, id_arguments, id_method;
+static ID id_eqq, id_next, id_result, id_lazy, id_receiver, id_arguments, id_method, id_source;
 static VALUE sym_each, sym_cycle;
 
 VALUE rb_eStopIteration;
@@ -567,6 +567,7 @@
     result = rb_block_call(obj, id_each, 0, 0, next_ii, obj);
     e->stop_exc = rb_exc_new2(rb_eStopIteration, "iteration reached an end");
     rb_ivar_set(e->stop_exc, id_result, result);
+    rb_ivar_set(e->stop_exc, id_source, obj);
     return rb_fiber_yield(1, &nil);
 }
 
@@ -1724,6 +1725,27 @@
     return rb_attr_get(self, id_result);
 }
 
+/*
+ * call-seq:
+ *   source       -> value
+ *
+ * Returns the enumerator responsible for raising this instance.
+ *
+ *   e = [].each
+ *
+ *   begin
+ *     e.next
+ *   rescue StopIteration => ex
+ *     puts ex.source
+ *   end
+ *
+ */
+static VALUE
+stop_source(VALUE self)
+{
+    return rb_attr_get(self, id_source);
+}
+
 void
 InitVM_Enumerator(void)
 {
@@ -1773,6 +1795,7 @@
 
     rb_eStopIteration = rb_define_class("StopIteration", rb_eIndexError);
     rb_define_method(rb_eStopIteration, "result", stop_result, 0);
+    rb_define_method(rb_eStopIteration, "source", stop_source, 0);
 
     /* Generator */
     rb_cGenerator = rb_define_class_under(rb_cEnumerator, "Generator", rb_cObject);
@@ -1808,6 +1831,7 @@
     id_receiver = rb_intern("receiver");
     id_arguments = rb_intern("arguments");
     id_method = rb_intern("method");
+    id_source = rb_intern("source");
     sym_each = ID2SYM(id_each);
     sym_cycle = ID2SYM(rb_intern("cycle"));
 
Index: test/ruby/test_enumerator.rb
===================================================================
--- test/ruby/test_enumerator.rb	(revision 36594)
+++ test/ruby/test_enumerator.rb	(working copy)
@@ -185,6 +185,16 @@
     assert_equal(res, exc.result)
   end
 
+  def test_stop_source
+    e = [].each
+    begin
+      e.next
+      fail
+    rescue StopIteration => ex
+      assert_equal(e, ex.source)
+    end      
+  end
+
   def test_next_values
     o = Object.new
     def o.each