diff --git a/ChangeLog b/ChangeLog
index df75f3e0d5..a735d2e57f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Mar 30 00:24:53 2011  Tanaka Akira  <akr@fsij.org>
+
+	* ext/stringio/stringio.c: parenthesize macro arguments.
+
 Tue Mar 29 21:51:31 2011  CHIKANAGA Tomoyuki  <nagachika00@gmail.com>
 
 	* object.c (rb_String): Kernel#String should call to_str before to_s.
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index 208fd4d76e..594813cbc0 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -30,7 +30,7 @@ struct StringIO {
 
 static void strio_init(int, VALUE *, struct StringIO *);
 
-#define IS_STRIO(obj) (rb_typeddata_is_kind_of(obj, &strio_data_type))
+#define IS_STRIO(obj) (rb_typeddata_is_kind_of((obj), &strio_data_type))
 #define error_inval(msg) (errno = EINVAL, rb_sys_fail(msg))
 
 static struct StringIO *
@@ -80,7 +80,7 @@ static const rb_data_type_t strio_data_type = {
     },
 };
 
-#define check_strio(self) ((struct StringIO*)rb_check_typeddata(self, &strio_data_type))
+#define check_strio(self) ((struct StringIO*)rb_check_typeddata((self), &strio_data_type))
 
 static struct StringIO*
 get_strio(VALUE self)