diff --git a/ChangeLog b/ChangeLog
index c02805bde3..74e37e2292 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Jun 15 19:54:21 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* bignum.c (big2str_find_n1): check integer overflow.
+
 Sun Jun 15 19:52:20 2008  Tanaka Akira  <akr@fsij.org>
 
 	* gc.c (STACK_LENGTH) [SPARC] : 0x80 offset removed.  [ruby-dev:33857]
diff --git a/bignum.c b/bignum.c
index 9a5b3c154a..70a88e64d9 100644
--- a/bignum.c
+++ b/bignum.c
@@ -652,6 +652,9 @@ rb_big2str0(x, base, trim)
     if (BIGZEROP(x)) {
 	return rb_str_new2("0");
     }
+    if (i >= LONG_MAX/SIZEOF_BDIGITS/CHAR_BIT) {
+	rb_raise(rb_eRangeError, "bignum too big to convert into `string'");
+    }
     j = SIZEOF_BDIGITS*CHAR_BIT*i;
     switch (base) {
       case 2: break;
diff --git a/test/ruby/test_bignum.rb b/test/ruby/test_bignum.rb
index c238337db5..e070a9c866 100644
--- a/test/ruby/test_bignum.rb
+++ b/test/ruby/test_bignum.rb
@@ -84,4 +84,12 @@ class TestBignum < Test::Unit::TestCase
     shift_test(-4518325415524767873)
     shift_test(-0xfffffffffffffffff)
   end
+
+  def test_too_big_to_s
+    if (big = 2**31-1).is_a?(Fixnum)
+      return
+    end
+    e = assert_raise(RangeError) {(1 << big).to_s}
+    assert_match(/too big to convert/, e.message)
+  end
 end
diff --git a/version.h b/version.h
index 480ca6c879..73b3fa9510 100644
--- a/version.h
+++ b/version.h
@@ -2,7 +2,7 @@
 #define RUBY_RELEASE_DATE "2008-06-15"
 #define RUBY_VERSION_CODE 186
 #define RUBY_RELEASE_CODE 20080615
-#define RUBY_PATCHLEVEL 183
+#define RUBY_PATCHLEVEL 184
 
 #define RUBY_VERSION_MAJOR 1
 #define RUBY_VERSION_MINOR 8