diff --git a/ChangeLog b/ChangeLog
index dc72f423837cfd..99fe86e3b8c79f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+Tue Oct 21 21:52:00 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* ext/zlib/zlib.c (rb_gzwriter_write): conversion should be done
+	  using to_str, not to_s.
+
+	* ext/zlib/zlib.c (rb_gzwriter_write): need proper conversion
+	  according to gz encoding.
+
+	* ext/zlib/zlib.c (rb_gzreader_ungetc): convert string encoding
+	  before unget.
+
 Tue Oct 21 21:33:36 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/test/unit.rb (assert_nothing_raised): raise with backtrace.
diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index 8d349c49ee61f4..bc0716b8357c0f 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -2747,10 +2747,10 @@ rb_gzwriter_write(VALUE obj, VALUE str)
 {
     struct gzfile *gz = get_gzfile(obj);
 
-    if (TYPE(str) != T_STRING) {
-       str = rb_obj_as_string(str);
+    StringValue(str);
+    if (gz->enc2 && gz->enc2 != rb_ascii8bit_encoding()) {
+	str = rb_str_conv_enc(str, rb_enc_get(str), gz->enc2);
     }
-    str = rb_str_export(str);
     gzfile_write(gz, (Bytef*)RSTRING_PTR(str), RSTRING_LEN(str));
     return INT2FIX(RSTRING_LEN(str));
 }
@@ -3075,6 +3075,11 @@ static VALUE
 rb_gzreader_ungetc(VALUE obj, VALUE s)
 {
     struct gzfile *gz = get_gzfile(obj);
+
+    StringValue(s);
+    if (gz->enc2 && gz->enc2 != rb_ascii8bit_encoding()) {
+	s = rb_str_conv_enc(s, rb_enc_get(s), gz->enc2);
+    }
     gzfile_ungets(gz, (const Bytef*)RSTRING_PTR(s), RSTRING_LEN(s));
     return Qnil;
 }
diff --git a/test/zlib/test_zlib.rb b/test/zlib/test_zlib.rb
index 5746f036ea5518..5a4a87a0fb5b6f 100644
--- a/test/zlib/test_zlib.rb
+++ b/test/zlib/test_zlib.rb
@@ -597,7 +597,7 @@ def test_write
       assert_equal("foo", Zlib::GzipReader.open(t.path) {|gz| gz.read })
 
       o = Object.new
-      def o.to_s; "bar"; end
+      def o.to_str; "bar"; end
       Zlib::GzipWriter.open(t.path) {|gz| gz.print(o) }
       assert_equal("bar", Zlib::GzipReader.open(t.path) {|gz| gz.read })
     end