diff --git a/libmat2/__init__.py b/libmat2/__init__.py
index 07d3036..91a51d8 100644
--- a/libmat2/__init__.py
+++ b/libmat2/__init__.py
@@ -1,6 +1,21 @@
 #!/bin/env python3
 
 # A set of extension that aren't supported, despite matching a supported mimetype
-unsupported_extensions = set(['bat', 'c', 'h', 'ksh', 'pl', 'txt', 'asc',
-                              'text', 'pot', 'brf', 'srt', 'rdf', 'wsdl',
-                              'xpdl', 'xsl', 'xsd'])
+unsupported_extensions = {
+    '.asc',
+    '.bat',
+    '.brf',
+    '.c',
+    '.h',
+    '.ksh',
+    '.pl',
+    '.pot',
+    '.rdf',
+    '.srt',
+    '.text',
+    '.txt',
+    '.wsdl',
+    '.xpdl',
+    '.xsd',
+    '.xsl',
+    }
diff --git a/tests/test_libmat2.py b/tests/test_libmat2.py
index 84eb75e..3d08dea 100644
--- a/tests/test_libmat2.py
+++ b/tests/test_libmat2.py
@@ -35,6 +35,14 @@ class TestUnsupportedFiles(unittest.TestCase):
         self.assertEqual(parser, None)
         os.remove('./tests/clean.py')
 
+class TestExplicitelyUnsupportedFiles(unittest.TestCase):
+    def test_pdf(self):
+        shutil.copy('./tests/test_libmat2.py', './tests/clean.txt')
+        parser, mimetype = parser_factory.get_parser('./tests/data/clean.txt')
+        self.assertEqual(mimetype, 'text/plain')
+        self.assertEqual(parser, None)
+        os.remove('./tests/clean.txt')
+
 
 class TestCorruptedFiles(unittest.TestCase):
     def test_pdf(self):