diff --git a/ChangeLog b/ChangeLog
index 69dfc40c1e..fa82e9f9f2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Sat Apr  9 21:54:15 2011  Shota Fukumori  <sorah@tubusu.net>
+
+	* ext/stringio/stringio.c (strio_each, strio_readlines):
+	  limit must not be zero. Fixes [ruby-dev:43392].
+
+	* test/stringio/test_stringio.rb: Add tests for above.
+
 Sat Apr  9 18:01:36 2011  Tanaka Akira  <akr@fsij.org>
 
 	* include/ruby/util.h: parenthesize macro arguments.
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index da4eb964cb..609355a51b 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -1067,6 +1067,11 @@ strio_each(int argc, VALUE *argv, VALUE self)
     struct StringIO *ptr = StringIO(self);
     VALUE line;
 
+    if(argc > 0 && TYPE(argv[argc-1]) == T_FIXNUM &&
+       FIX2INT(argv[argc-1]) == 0) {
+	rb_raise(rb_eArgError, "invalid limit: 0 for readlines");
+    }
+
     RETURN_ENUMERATOR(self, argc, argv);
 
     while (!NIL_P(line = strio_getline(argc, argv, readable(ptr)))) {
@@ -1088,6 +1093,12 @@ strio_readlines(int argc, VALUE *argv, VALUE self)
 {
     struct StringIO *ptr = StringIO(self);
     VALUE ary = rb_ary_new(), line;
+
+    if(argc > 0 && TYPE(argv[argc-1]) == T_FIXNUM &&
+       FIX2INT(argv[argc-1]) == 0) {
+	rb_raise(rb_eArgError, "invalid limit: 0 for readlines");
+    }
+
     while (!NIL_P(line = strio_getline(argc, argv, readable(ptr)))) {
 	rb_ary_push(ary, line);
     }
diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index c581681817..8bf6c595a0 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -482,4 +482,12 @@ class TestStringIO < Test::Unit::TestCase
     assert_raise(RuntimeError, bug) {s.string = "foo"}
     assert_raise(RuntimeError, bug) {s.reopen("")}
   end
+
+  def test_readlines_limit_0
+    assert_raise(ArgumentError, "[ruby-dev:43392]") { StringIO.new.readlines(0) }
+  end
+
+  def test_each_line_limit_0
+    assert_raise(ArgumentError, "[ruby-dev:43392]") { StringIO.new.each_line(0) }
+  end
 end