diff --git a/ChangeLog b/ChangeLog
index 725dd266e2..3f47ae576b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jun 26 12:48:37 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* transcode.c (load_transcoder_entry): fix transcoder loading race
+	  condition, by waiting in require.  [ruby-dev:49106] [Bug #11277]
+
 Fri Jun 26 07:53:56 2015  Eric Wong  <e@80x24.org>
 
 	* enum.c (enum_minmax): simplify return value creation
diff --git a/test/ruby/test_transcode.rb b/test/ruby/test_transcode.rb
index 0306dc3e87..8ace00c172 100644
--- a/test/ruby/test_transcode.rb
+++ b/test/ruby/test_transcode.rb
@@ -2091,4 +2091,22 @@ class TestTranscode < Test::Unit::TestCase
     assert_equal("\x00\x00\xFE\xFF\x00\x00\x00t\x00\x00\x00e\x00\x00\x00s\x00\x00\x00t", result.b, bug)
     end;
   end
+
+  def test_loading_race
+    assert_separately([], <<-'end;') #do
+      bug11277 = '[ruby-dev:49106] [Bug #11277]'
+      num = 2
+      th = (0...num).map do |i|
+        Thread.new {"\u3042".encode("EUC-JP")}
+      end
+      result = nil
+      assert_warning("", bug11277) do
+        assert_nothing_raised(Encoding::ConverterNotFoundError, bug11277) do
+          result = th.map(&:value)
+        end
+      end
+      expected = "\xa4\xa2".force_encoding(Encoding::EUC_JP)
+      assert_equal([expected]*num, result, bug11277)
+    end;
+  end
 end
diff --git a/transcode.c b/transcode.c
index 17d406e8be..b9d0adc553 100644
--- a/transcode.c
+++ b/transcode.c
@@ -370,15 +370,12 @@ load_transcoder_entry(transcoder_entry_t *entry)
         char *const path = RSTRING_PTR(fn);
 	const int safe = rb_safe_level();
 
-        entry->lib = NULL;
-
         memcpy(path, transcoder_lib_prefix, sizeof(transcoder_lib_prefix) - 1);
         memcpy(path + sizeof(transcoder_lib_prefix) - 1, lib, len);
         rb_str_set_len(fn, total_len);
         FL_UNSET(fn, FL_TAINT);
         OBJ_FREEZE(fn);
-        if (!rb_require_safe(fn, safe > 3 ? 3 : safe))
-            return NULL;
+        rb_require_safe(fn, safe > 3 ? 3 : safe);
     }
 
     if (entry->transcoder)