diff --git a/django/contrib/auth/tokens.py b/django/contrib/auth/tokens.py
index c534f304f3..c3863d1dea 100644
--- a/django/contrib/auth/tokens.py
+++ b/django/contrib/auth/tokens.py
@@ -1,4 +1,4 @@
-from datetime import datetime
+from datetime import datetime, time
 
 from django.conf import settings
 from django.utils.crypto import constant_time_compare, salted_hmac
@@ -36,6 +36,8 @@ class PasswordResetTokenGenerator:
         # Parse the token
         try:
             ts_b36, _ = token.split("-")
+            # RemovedInDjango40Warning.
+            legacy_token = len(ts_b36) < 4
         except ValueError:
             return False
 
@@ -55,8 +57,14 @@ class PasswordResetTokenGenerator:
             ):
                 return False
 
+        # RemovedInDjango40Warning: convert days to seconds and round to
+        # midnight (server time) for pre-Django 3.1 tokens.
+        now = self._now()
+        if legacy_token:
+            ts *= 24 * 60 * 60
+            ts += int((now - datetime.combine(now.date(), time.min)).total_seconds())
         # Check the timestamp is within limit.
-        if (self._num_seconds(self._now()) - ts) > settings.PASSWORD_RESET_TIMEOUT:
+        if (self._num_seconds(now) - ts) > settings.PASSWORD_RESET_TIMEOUT:
             return False
 
         return True
diff --git a/docs/releases/3.1.3.txt b/docs/releases/3.1.3.txt
index 9c58586f46..6f526aa5c9 100644
--- a/docs/releases/3.1.3.txt
+++ b/docs/releases/3.1.3.txt
@@ -48,3 +48,6 @@ Bugfixes
 
 * Fixed a regression in Django 3.1.2 that caused incorrect form input layout on
   small screens in the admin change form view (:ticket:`32069`).
+
+* Fixed a regression in Django 3.1 that invalidated pre-Django 3.1 password
+  reset tokens (:ticket:`32130`).
diff --git a/tests/auth_tests/test_tokens.py b/tests/auth_tests/test_tokens.py
index 42ac71148e..a9ba0e200f 100644
--- a/tests/auth_tests/test_tokens.py
+++ b/tests/auth_tests/test_tokens.py
@@ -1,4 +1,4 @@
-from datetime import datetime, timedelta
+from datetime import date, datetime, timedelta
 
 from django.conf import settings
 from django.contrib.auth.models import User
@@ -86,6 +86,27 @@ class TokenGeneratorTest(TestCase):
             )
             self.assertIs(p4.check_token(user, tk1), False)
 
+    def test_legacy_days_timeout(self):
+        # RemovedInDjango40Warning: pre-Django 3.1 tokens will be invalid.
+        class LegacyPasswordResetTokenGenerator(MockedPasswordResetTokenGenerator):
+            """Pre-Django 3.1 tokens generator."""
+            def _num_seconds(self, dt):
+                # Pre-Django 3.1 tokens use days instead of seconds.
+                return (dt.date() - date(2001, 1, 1)).days
+
+        user = User.objects.create_user('tokentestuser', 'test2@example.com', 'testpw')
+        now = datetime.now()
+        p0 = LegacyPasswordResetTokenGenerator(now)
+        tk1 = p0.make_token(user)
+        p1 = MockedPasswordResetTokenGenerator(
+            now + timedelta(seconds=settings.PASSWORD_RESET_TIMEOUT),
+        )
+        self.assertIs(p1.check_token(user, tk1), True)
+        p2 = MockedPasswordResetTokenGenerator(
+            now + timedelta(seconds=(settings.PASSWORD_RESET_TIMEOUT + 24 * 60 * 60)),
+        )
+        self.assertIs(p2.check_token(user, tk1), False)
+
     def test_check_token_with_nonexistent_token_and_user(self):
         user = User.objects.create_user('tokentestuser', 'test2@example.com', 'testpw')
         p0 = PasswordResetTokenGenerator()