diff --git a/kittengroomer/helpers.py b/kittengroomer/helpers.py
index da6f401..45ba4e9 100644
--- a/kittengroomer/helpers.py
+++ b/kittengroomer/helpers.py
@@ -251,7 +251,7 @@ class FileBase(object):
         return mimetype
 
     def _split_mimetype(self, mimetype):
-        if '/' in mimetype:
+        if mimetype and '/' in mimetype:
             main_type, sub_type = mimetype.split('/')
         else:
             main_type, sub_type = None, None
diff --git a/tests/test_kittengroomer.py b/tests/test_kittengroomer.py
index 37c8b9d..dc6c35d 100644
--- a/tests/test_kittengroomer.py
+++ b/tests/test_kittengroomer.py
@@ -124,7 +124,7 @@ class TestFileBase:
         with mock.patch('kittengroomer.helpers.magic.from_file',
                         return_value='text/plain'):
             file = FileBase('', '')
-            file.mimetype = 'text/plain'
+        assert file.mimetype == 'text/plain'
 
     def test_maintype_and_subtype_attributes(self):
         """If a file has a full mimetype, maintype and subtype should ==
@@ -142,6 +142,13 @@ class TestFileBase:
             file = FileBase('', '')
         assert file.has_mimetype is False
 
+    def test_has_mimetype_mimetype_is_none(self):
+        """If a file doesn't have a full mimetype has_mimetype should == False."""
+        with mock.patch('kittengroomer.helpers.FileBase._determine_mimetype',
+                        return_value=None):
+            file = FileBase('', '')
+        assert file.has_mimetype is False
+
     # File properties
 
     def get_property_doesnt_exist(self, text_file):