diff --git a/ChangeLog b/ChangeLog
index 001a77951d..8e055629cb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Dec  1 23:14:04 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* thread.c (rb_thread_setname): check the argument if valid
+	  string.  [ruby-core:71774] [Bug #11756]
+
 Tue Dec  1 17:13:41 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* string.c (rb_string_value_cstr): should not raise on frozen
diff --git a/test/ruby/test_thread.rb b/test/ruby/test_thread.rb
index d076494cdf..78ed329274 100644
--- a/test/ruby/test_thread.rb
+++ b/test/ruby/test_thread.rb
@@ -1057,4 +1057,22 @@ q.pop
     t.kill
     t.join
   end
+
+  def test_thread_invalid_name
+    bug11756 = '[ruby-core:71774] [Bug #11756]'
+    t = Thread.start {}
+    assert_raise(ArgumentError, bug11756) {t.name = "foo\0bar"}
+  ensure
+    t.kill
+    t.join
+  end
+
+  def test_thread_invalid_object
+    bug11756 = '[ruby-core:71774] [Bug #11756]'
+    t = Thread.start {}
+    assert_raise(TypeError, bug11756) {t.name = nil}
+  ensure
+    t.kill
+    t.join
+  end
 end
diff --git a/thread.c b/thread.c
index 7190a943bd..62713e80aa 100644
--- a/thread.c
+++ b/thread.c
@@ -2776,6 +2776,7 @@ rb_thread_setname(VALUE thread, VALUE name)
 {
     rb_thread_t *th;
     GetThreadPtr(thread, th);
+    StringValueCStr(name);
     th->name = rb_str_new_frozen(name);
 #if defined(HAVE_PTHREAD_SETNAME_NP)
 # if defined(__linux__)