diff --git a/ChangeLog b/ChangeLog
index 4e523fdbce..a8bd225f09 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Nov 29 16:06:04 2004  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/stringio/stringio.c (strio_write): insufficiently filled string
+	  being extended when overwriting.  [ruby-core:03836]
+
 Mon Nov 29 15:22:28 2004  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* test/io/nonblock/test_flush.rb: abandon tests when io/nonblock is
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index 4d960c4ea3..f46af0f0ad 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -794,7 +794,7 @@ strio_write(self, str)
     else {
 	if (ptr->pos + len > olen) {
 	    rb_str_resize(ptr->string, ptr->pos + len);
-	    MEMZERO(RSTRING(ptr->string)->ptr + olen, char, ptr->pos - olen);
+	    MEMZERO(RSTRING(ptr->string)->ptr + olen, char, ptr->pos + len - olen);
 	}
 	else {
 	    rb_str_modify(ptr->string);
diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index fee305e856..de15ab5508 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -30,4 +30,14 @@ class TestStringIO < Test::Unit::TestCase
     io.print "last"
     assert_equal("\0" * n + "last", io.string)
   end
+
+  def test_overwrite # [ruby-core:03836]
+    stringio = StringIO.new
+    responses = ['', 'just another ruby', 'hacker']
+    responses.each do |resp|
+      stringio.puts(resp)
+      stringio.rewind
+    end
+    assert_equal("hacker\nother ruby\n", stringio.string)
+  end
 end