diff --git a/ChangeLog b/ChangeLog
index 8e055629cb..d9b369b993 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Tue Dec  1 23:36:39 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* thread.c (rb_thread_setname): allow to reset thread name.
+
 Tue Dec  1 23:14:04 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* thread.c (rb_thread_setname): check the argument if valid
diff --git a/test/ruby/test_thread.rb b/test/ruby/test_thread.rb
index 78ed329274..0affca294a 100644
--- a/test/ruby/test_thread.rb
+++ b/test/ruby/test_thread.rb
@@ -1050,9 +1050,14 @@ q.pop
   end
 
   def test_thread_name
-    t = Thread.start { sleep }
+    t = Thread.start {}
+    assert_nil t.name
+    s = t.inspect
     t.name = 'foo'
     assert_equal 'foo', t.name
+    t.name = nil
+    assert_nil t.name
+    assert_equal s, t.inspect
   ensure
     t.kill
     t.join
@@ -1070,7 +1075,7 @@ q.pop
   def test_thread_invalid_object
     bug11756 = '[ruby-core:71774] [Bug #11756]'
     t = Thread.start {}
-    assert_raise(TypeError, bug11756) {t.name = nil}
+    assert_raise(TypeError, bug11756) {t.name = []}
   ensure
     t.kill
     t.join
diff --git a/thread.c b/thread.c
index 62713e80aa..6f41de3d73 100644
--- a/thread.c
+++ b/thread.c
@@ -2774,18 +2774,23 @@ rb_thread_getname(VALUE thread)
 static VALUE
 rb_thread_setname(VALUE thread, VALUE name)
 {
+    const char *s = "";
     rb_thread_t *th;
     GetThreadPtr(thread, th);
-    StringValueCStr(name);
-    th->name = rb_str_new_frozen(name);
+    if (!NIL_P(name)) {
+	StringValueCStr(name);
+	name = rb_str_new_frozen(name);
+	s = RSTRING_PTR(name);
+    }
+    th->name = name;
 #if defined(HAVE_PTHREAD_SETNAME_NP)
 # if defined(__linux__)
-    pthread_setname_np(th->thread_id, RSTRING_PTR(name));
+    pthread_setname_np(th->thread_id, s);
 # elif defined(__NetBSD__)
-    pthread_setname_np(th->thread_id, RSTRING_PTR(name), "%s");
+    pthread_setname_np(th->thread_id, s, "%s");
 # endif
 #elif defined(HAVE_PTHREAD_SET_NAME_NP) /* FreeBSD */
-    pthread_set_name_np(th->thread_id, RSTRING_PTR(name));
+    pthread_set_name_np(th->thread_id, s);
 #endif
     return name;
 }