diff --git a/ChangeLog b/ChangeLog
index 5d0cea97c5..8615829430 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Jan 28 21:49:30 2011  Tanaka Akira  <akr@fsij.org>
+
+	* ext/zlib/zlib.c: parenthesize macro arguments.
+
 Fri Jan 28 17:47:33 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* test/gdbm/test_gdbm.rb (TestGDBM2#test_writer_open_notexist):
diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index 1c14411096..f119a17bf6 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -1787,7 +1787,7 @@ struct gzfile {
 #define GZFILE_FLAG_FOOTER_FINISHED  (ZSTREAM_FLAG_UNUSED << 2)
 
 #define GZFILE_IS_FINISHED(gz) \
-    (ZSTREAM_IS_FINISHED(&gz->z) && (gz)->z.buf_filled == 0)
+    (ZSTREAM_IS_FINISHED(&(gz)->z) && (gz)->z.buf_filled == 0)
 
 #define GZFILE_READ_SIZE  2048