diff --git a/ChangeLog b/ChangeLog
index 84e93545d8..bf70701572 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Jun 12 02:36:52 2016  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* regcomp.c (compile_length_tree): return error code immediately
+	  if compile_length_tree raised error [Bug #12418]
+
 Sun Jun 12 02:27:07 2016  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* thread.c (recursive_list_access): a object id may be a Bignum.  so,
diff --git a/regcomp.c b/regcomp.c
index 23cb0ead9a..34b37f8e4c 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -1592,13 +1592,15 @@ compile_length_tree(Node* node, regex_t* reg)
 
   case NT_ALT:
     {
-      int n;
-
-      n = r = 0;
+      int n = 0;
+      len = 0;
       do {
-	r += compile_length_tree(NCAR(node), reg);
-	n++;
+        r = compile_length_tree(NCAR(node), reg);
+        if (r < 0) return r;
+        len += r;
+        n++;
       } while (IS_NOT_NULL(node = NCDR(node)));
+      r = len;
       r += (SIZE_OP_PUSH + SIZE_OP_JUMP) * (n - 1);
     }
     break;
diff --git a/test/ruby/test_regexp.rb b/test/ruby/test_regexp.rb
index 96b0bfacb1..db6e8a3b81 100644
--- a/test/ruby/test_regexp.rb
+++ b/test/ruby/test_regexp.rb
@@ -1003,6 +1003,9 @@ class TestRegexp < Test::Unit::TestCase
     conds = {"xy"=>true, "yx"=>true, "xx"=>false, "yy"=>false}
     assert_match_each(/\A((x)|(y))(?(2)y|x)\z/, conds, bug8583)
     assert_match_each(/\A((?<x>x)|(?<y>y))(?(<x>)y|x)\z/, conds, bug8583)
+
+    bug12418 = '[ruby-core:75694] [Bug #12418]'
+    assert_raise(RegexpError, bug12418){ Regexp.new('(0?0|(?(5)||)|(?(5)||))?') }
   end
 
   def test_options_in_look_behind
diff --git a/version.h b/version.h
index ce44dd3ff7..25a99464db 100644
--- a/version.h
+++ b/version.h
@@ -1,6 +1,6 @@
 #define RUBY_VERSION "2.3.2"
 #define RUBY_RELEASE_DATE "2016-06-12"
-#define RUBY_PATCHLEVEL 122
+#define RUBY_PATCHLEVEL 123
 
 #define RUBY_RELEASE_YEAR 2016
 #define RUBY_RELEASE_MONTH 6