From 63794da99d8fa2fa8ae7731073d97893ab130a06 Mon Sep 17 00:00:00 2001
From: Jock Tanner <tanner.of.kha@gmail.com>
Date: Wed, 26 Feb 2020 23:51:27 +1000
Subject: [PATCH 1/2] Fix descending choice building in OrderingFilter.

---
 django_filters/filters.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/django_filters/filters.py b/django_filters/filters.py
index 7331bfd1d..40958253d 100644
--- a/django_filters/filters.py
+++ b/django_filters/filters.py
@@ -737,12 +737,13 @@ def normalize_fields(cls, fields):
         ])
 
     def build_choices(self, fields, labels):
+        fields = {param: field for field, param in fields.items()}
         ascending = [
             (param, labels.get(field, _(pretty_name(param))))
-            for field, param in fields.items()
+            for param, field in fields.items()
         ]
         descending = [
-            ('-%s' % param, labels.get('-%s' % param, self.descending_fmt % label))
+            ('-%s' % param, labels.get('-%s' % fields[param], self.descending_fmt % label))
             for param, label in ascending
         ]
 

From 2fb594059a77f890424ac00130e9197f23b62b2b Mon Sep 17 00:00:00 2001
From: Jock Tanner <tanner.of.kha@gmail.com>
Date: Wed, 26 Feb 2020 23:52:22 +1000
Subject: [PATCH 2/2] Modify test case.

---
 tests/test_filters.py | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/tests/test_filters.py b/tests/test_filters.py
index d2061f19f..22233abc0 100644
--- a/tests/test_filters.py
+++ b/tests/test_filters.py
@@ -1508,17 +1508,19 @@ def test_field_labels(self):
 
     def test_field_labels_descending(self):
         f = OrderingFilter(
-            fields=['username'],
+            fields=(('a', 'c'), ('b', 'd')),
             field_labels={
-                'username': 'BLABLA',
-                '-username': 'XYZXYZ',
+                '-a': 'BLABLA',
+                '-b': 'XYZXYZ',
             }
         )
 
         self.assertEqual(list(f.field.choices), [
             ('', '---------'),
-            ('username', 'BLABLA'),
-            ('-username', 'XYZXYZ'),
+            ('c', 'C'),
+            ('-c', 'BLABLA'),
+            ('d', 'D'),
+            ('-d', 'XYZXYZ'),
         ])
 
     def test_normalize_fields(self):