diff --git a/ext/date/date_parse.c b/ext/date/date_parse.c
index 597c25a..883f74e 100644
--- a/ext/date/date_parse.c
+++ b/ext/date/date_parse.c
@@ -2098,6 +2098,7 @@ date__xmlschema(VALUE str)
     rb_match_busy(backref);
 
     hash = rb_hash_new();
+    str  = rb_str_dup(str);
 
     if (xmlschema_datetime(str, hash))
 	goto ok;
@@ -2169,6 +2170,7 @@ date__rfc2822(VALUE str)
     rb_match_busy(backref);
 
     hash = rb_hash_new();
+    str = rb_str_dup(str);
     rfc2822(str, hash);
     rb_backref_set(backref);
     return hash;
@@ -2315,6 +2317,7 @@ date__httpdate(VALUE str)
     rb_match_busy(backref);
 
     hash = rb_hash_new();
+    str = rb_str_dup(str);
 
     if (httpdate_type1(str, hash))
 	goto ok;
diff --git a/test/date/test_date_parse.rb b/test/date/test_date_parse.rb
index fb54d14..3ef5716 100644
--- a/test/date/test_date_parse.rb
+++ b/test/date/test_date_parse.rb
@@ -1019,6 +1019,20 @@ class TestDateParse < Test::Unit::TestCase
     assert_equal(Date::ITALY + 10, d.start)
   end
 
+  def test_date_xmlschema_does_not_mutate
+    x = "2006-02-13T10:37:00.000-05:00"
+    y = x.dup
+    Date.xmlschema x
+    assert_equal y, x
+  end
+
+  def test_datetime_xmlschema_does_not_mutate
+    x = "2006-02-13T10:37:00.000-05:00"
+    y = x.dup
+    DateTime.xmlschema x
+    assert_equal y, x
+  end
+
   def test_rfc2822
     assert_instance_of(Date, Date.rfc2822)
     assert_instance_of(DateTime, DateTime.rfc2822)
@@ -1034,6 +1048,17 @@ class TestDateParse < Test::Unit::TestCase
     assert_equal(Date::ITALY + 10, d.start)
   end
 
+  def test_rfc2822_does_not_mutate
+    x = 'Mon, 1 Jan -4712 00:00:00 +0000'
+    y = x.dup
+
+    Date.rfc2822 x
+    assert_equal y, x
+
+    DateTime.rfc2822 x
+    assert_equal y, x
+  end
+
   def test_httpdate
     assert_instance_of(Date, Date.httpdate)
     assert_instance_of(DateTime, DateTime.httpdate)
@@ -1047,6 +1072,17 @@ class TestDateParse < Test::Unit::TestCase
     assert_equal(Date::ITALY + 10, d.start)
   end
 
+  def test_httpdate_does_not_mutate
+    x = "Mon, 01 Jan -4712 00:00:00 GMT"
+    y = x.dup
+
+    Date.httpdate x
+    assert_equal y, x
+
+    DateTime.httpdate x
+    assert_equal y, x
+  end
+
   def test_jisx0301
     assert_instance_of(Date, Date.jisx0301)
     assert_instance_of(DateTime, DateTime.jisx0301)