diff --git a/ChangeLog b/ChangeLog
index 8f84f812fd..bdffa1e568 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Mar 18 17:17:36 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* gc.c (free_method_entry_i): method entry may be in
+	  unlinked_method_entry_list.  [ruby-core:43383][Bug #6171]
+
 Sun Mar 18 15:27:31 2012  Tanaka Akira  <akr@fsij.org>
 
 	* compile.c: typo fix by Run Paint Run Run.
diff --git a/gc.c b/gc.c
index cd136cb4dd..76f58ee0e6 100644
--- a/gc.c
+++ b/gc.c
@@ -1709,7 +1709,9 @@ mark_m_tbl(rb_objspace_t *objspace, st_table *tbl, int lev)
 static int
 free_method_entry_i(ID key, rb_method_entry_t *me, st_data_t data)
 {
-    rb_free_method_entry(me);
+    if (!me->mark) {
+	rb_free_method_entry(me);
+    }
     return ST_CONTINUE;
 }
 
diff --git a/test/ruby/test_method.rb b/test/ruby/test_method.rb
index c784bd357e..ed04570e6a 100644
--- a/test/ruby/test_method.rb
+++ b/test/ruby/test_method.rb
@@ -461,4 +461,16 @@ class TestMethod < Test::Unit::TestCase
     assert_nothing_raised { v.instance_eval { mv2 } }
     assert_nothing_raised { v.instance_eval { mv3 } }
   end
+
+  def test_bound_method_entry
+    bug6171 = '[ruby-core:43383]'
+    assert_ruby_status([], <<-EOC, bug6171)
+      class Bug6171
+        def initialize(target)
+          define_singleton_method(:reverse, target.method(:reverse).to_proc)
+        end
+      end
+      1000.times {p = Bug6171.new('test'); 10000.times {p.reverse}}
+      EOC
+  end
 end