diff --git a/ChangeLog b/ChangeLog
index 2284a5f770..5ea7021cdf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Nov 24 02:03:30 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* iseq.c (rb_insn_operand_intern): preserve encoding of method
+	  name in CALL_INFO at disassembling.
+
 Mon Nov 24 02:02:59 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* io.c (must_respond_to): preserve encodings of variable name and
diff --git a/iseq.c b/iseq.c
index 08a7918353..f290ed4692 100644
--- a/iseq.c
+++ b/iseq.c
@@ -1230,7 +1230,7 @@ rb_insn_operand_intern(const rb_iseq_t *iseq,
 	    VALUE ary = rb_ary_new();
 
 	    if (ci->mid) {
-		rb_ary_push(ary, rb_sprintf("mid:%s", rb_id2name(ci->mid)));
+		rb_ary_push(ary, rb_sprintf("mid:%"PRIsVALUE, rb_id2str(ci->mid)));
 	    }
 
 	    rb_ary_push(ary, rb_sprintf("argc:%d", ci->orig_argc));
diff --git a/test/ruby/test_iseq.rb b/test/ruby/test_iseq.rb
index 79c41bb900..d7d15c7703 100644
--- a/test/ruby/test_iseq.rb
+++ b/test/ruby/test_iseq.rb
@@ -52,13 +52,14 @@ class TestISeq < Test::Unit::TestCase
   end if defined?(RubyVM::InstructionSequence.load)
 
   def test_disasm_encoding
-    src = "\u{3042} = 1; \u{3042}"
-    enc, Encoding.default_internal = Encoding.default_internal, src.encoding
-    assert_equal(src.encoding, RubyVM::InstructionSequence.compile(src).disasm.encoding)
+    src = "\u{3042} = 1; \u{3042}; \u{3043}"
+    asm = RubyVM::InstructionSequence.compile(src).disasm
+    assert_equal(src.encoding, asm.encoding)
+    assert_predicate(asm, :valid_encoding?)
     src.encode!(Encoding::Shift_JIS)
-    assert_equal(true, RubyVM::InstructionSequence.compile(src).disasm.ascii_only?)
-  ensure
-    Encoding.default_internal = enc
+    asm = RubyVM::InstructionSequence.compile(src).disasm
+    assert_equal(src.encoding, asm.encoding)
+    assert_predicate(asm, :valid_encoding?)
   end
 
   LINE_BEFORE_METHOD = __LINE__