diff --git a/ChangeLog b/ChangeLog
index 54ca99cc10..0a54e6b66d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon May 12 13:57:19 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* eval.c (is_defined): add NODE_OP_ASGN_{OR,AND}.  "defined?(a||=1)"
+	  should not operate assignment.  [ruby-dev:34645]
+
 Mon May 12 12:59:23 2008  Hidetoshi NAGAI  <nagai@ai.kyutech.ac.jp>
 
 	* ext/tk/lib/tk/wm.rb: Wm#overrideredirect overwrites arguemnt to
diff --git a/eval.c b/eval.c
index 75e85bf494..c419230c15 100644
--- a/eval.c
+++ b/eval.c
@@ -2440,6 +2440,8 @@ is_defined(self, node, buf)
       case NODE_ATTRSET:
       case NODE_OP_ASGN1:
       case NODE_OP_ASGN2:
+      case NODE_OP_ASGN_OR:
+      case NODE_OP_ASGN_AND:
       case NODE_MASGN:
       case NODE_LASGN:
       case NODE_DASGN: