diff --git a/ChangeLog b/ChangeLog
index 1d2906347f..a8ef50bc79 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 13:29:26 2008  Tanaka Akira  <akr@fsij.org>
 
 	* bignum.c (bigzero_p): check from MSB to LSB.  [ruby-dev:34649]
diff --git a/compile.c b/compile.c
index 93bcb8a12f..e29d6aedd3 100644
--- a/compile.c
+++ b/compile.c
@@ -2473,6 +2473,8 @@ defined_expr(rb_iseq_t *iseq, LINK_ANCHOR *ret,
 
       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: