diff --git a/ChangeLog b/ChangeLog
index 1b8db0dc6e..22eceac578 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Wed Apr 21 00:16:44 2010  Yusuke Endoh  <mame@tsg.ne.jp>
+
+	* ext/zlib/zlib.c (rb_deflate_params): update buf_filled count because
+	  deflateParams writes to out buffer.  And, revert r18029 because the
+	  flush was not needed now and emits garbage.  [ruby-dev:40802]
+
 Wed Apr 21 00:01:05 2010  Yusuke Endoh  <mame@tsg.ne.jp>
 
 	* vm_method.c (rb_add_method_def): decrement alias count of
diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index 435a1a6a9f..8c3af3dfe7 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -1371,16 +1371,20 @@ rb_deflate_params(VALUE obj, VALUE v_level, VALUE v_strategy)
     struct zstream *z = get_zstream(obj);
     int level, strategy;
     int err;
+    uInt n;
 
     level = ARG_LEVEL(v_level);
     strategy = ARG_STRATEGY(v_strategy);
 
-    zstream_run(z, (Bytef*)"", 0, Z_SYNC_FLUSH);
+    n = z->stream.avail_out;
     err = deflateParams(&z->stream, level, strategy);
+    z->buf_filled += n - z->stream.avail_out;
     while (err == Z_BUF_ERROR) {
 	rb_warning("deflateParams() returned Z_BUF_ERROR");
 	zstream_expand_buffer(z);
+	n = z->stream.avail_out;
 	err = deflateParams(&z->stream, level, strategy);
+	z->buf_filled += n - z->stream.avail_out;
     }
     if (err != Z_OK) {
 	raise_zlib_error(err, z->stream.msg);