diff --git a/rangefilter/filter.py b/rangefilter/filter.py
index 91015db..cfe529e 100644
--- a/rangefilter/filter.py
+++ b/rangefilter/filter.py
@@ -20,6 +20,7 @@ from django.utils import timezone
 from django.template.defaultfilters import slugify
 from django.templatetags.static import StaticNode
 from django.utils.translation import ugettext as _
+from django.utils.encoding import force_text
 from django.contrib.admin.widgets import AdminDateWidget, AdminSplitDateTime as BaseAdminSplitDateTime
 
 
@@ -57,7 +58,7 @@ class DateRangeFilter(admin.filters.FieldListFilter):
             # slugify converts any non-unicode characters to empty characters
             # but system_name is required, if title converts to empty string use id
             # https://github.com/silentsokolov/django-admin-rangefilter/issues/18
-            'system_name': slugify(self.title) if slugify(self.title) else id(self.title),
+            'system_name': force_text(slugify(self.title) if slugify(self.title) else id(self.title)),
             'query_string': cl.get_query_string(
                 {}, remove=self._get_expected_fields()
             )
@@ -127,7 +128,8 @@ class DateRangeFilter(admin.filters.FieldListFilter):
         return form_class
 
     def _get_form_fields(self):
-        return OrderedDict((
+        return OrderedDict(
+            (
                 (self.lookup_kwarg_gte, forms.DateField(
                     label='',
                     widget=AdminDateWidget(attrs={'placeholder': _('From date')}),
@@ -140,7 +142,8 @@ class DateRangeFilter(admin.filters.FieldListFilter):
                     localize=True,
                     required=False
                 )),
-        ))
+            )
+        )
 
     @staticmethod
     def get_js():
@@ -174,7 +177,8 @@ class DateTimeRangeFilter(DateRangeFilter):
         return expected_fields
 
     def _get_form_fields(self):
-        return OrderedDict((
+        return OrderedDict(
+            (
                 (self.lookup_kwarg_gte, forms.SplitDateTimeField(
                     label='',
                     widget=AdminSplitDateTime(attrs={'placeholder': _('From date')}),
@@ -187,7 +191,8 @@ class DateTimeRangeFilter(DateRangeFilter):
                     localize=True,
                     required=False
                 )),
-        ))
+            )
+        )
 
     def _make_query_filter(self, request, validated_data):
         query_params = {}
diff --git a/setup.py b/setup.py
index bf1959d..6b91a41 100755
--- a/setup.py
+++ b/setup.py
@@ -59,6 +59,7 @@ setup(
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
         'Topic :: Utilities',
     ],
 )