diff --git a/glymur/jp2k.py b/glymur/jp2k.py
index ea3c859..2994742 100644
--- a/glymur/jp2k.py
+++ b/glymur/jp2k.py
@@ -238,7 +238,7 @@ class Jp2k(Jp2kBox):
         outfile += b'0' * num_pad_bytes
         cparams.outfile = outfile
 
-        if self.filename[-4:].lower() == '.jp2':
+        if self.filename[-4:].endswith(('.jp2', '.JP2')):
             cparams.codec_fmt = opj2.CODEC_JP2
         else:
             cparams.codec_fmt = opj2.CODEC_J2K
diff --git a/glymur/test/test_jp2k.py b/glymur/test/test_jp2k.py
index 8b04dfa..c018897 100644
--- a/glymur/test/test_jp2k.py
+++ b/glymur/test/test_jp2k.py
@@ -224,6 +224,17 @@ class TestJp2k(unittest.TestCase):
             filename = 'this file does not actually exist on the file system.'
             Jp2k(filename)
 
+    @unittest.skipIf(os.name == "nt", "NamedTemporaryFile issue on windows")
+    def test_write_with_JP2_suffix(self):
+        """should be able to write with JP2 suffix."""
+        j2k = Jp2k(self.j2kfile)
+        expdata = j2k.read()
+        with tempfile.NamedTemporaryFile(suffix='.JP2') as tfile:
+            ofile = Jp2k(tfile.name, 'wb')
+            ofile.write(expdata)
+            actdata = ofile.read()
+            np.testing.assert_array_equal(actdata, expdata)
+
     @unittest.skipIf(os.name == "nt", "NamedTemporaryFile issue on windows")
     def test_write_srgb_without_mct(self):
         """should be able to write RGB without specifying mct"""