diff --git a/django/db/models/query_utils.py b/django/db/models/query_utils.py
index 0caa165e151b..6917820604b4 100644
--- a/django/db/models/query_utils.py
+++ b/django/db/models/query_utils.py
@@ -217,6 +217,7 @@ def _unregister_lookup(cls, lookup, lookup_name=None):
         if lookup_name is None:
             lookup_name = lookup.lookup_name
         del cls.class_lookups[lookup_name]
+        cls._clear_cached_lookups()
 
 
 def select_related_descend(field, restricted, requested, load_fields, reverse=False):
diff --git a/tests/custom_lookups/tests.py b/tests/custom_lookups/tests.py
index 1cf99b8300da..943c99f18f76 100644
--- a/tests/custom_lookups/tests.py
+++ b/tests/custom_lookups/tests.py
@@ -324,6 +324,8 @@ def test_lookups_caching(self):
             # getting the lookups again should re-cache
             self.assertIn("exactly", field.get_lookups())
 
+        self.assertNotIn("exactly", field.get_lookups())
+
 
 class BilateralTransformTests(TestCase):
     def test_bilateral_upper(self):
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index fa59a3e0b137..68e008cd5bb6 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -2770,16 +2770,20 @@ def test_func_unique_constraint_lookups(self):
             with connection.schema_editor() as editor:
                 editor.add_constraint(Author, constraint)
                 sql = constraint.create_sql(Author, editor)
-        table = Author._meta.db_table
-        constraints = self.get_constraints(table)
-        self.assertIn(constraint.name, constraints)
-        self.assertIs(constraints[constraint.name]["unique"], True)
-        # SQL contains columns.
-        self.assertIs(sql.references_column(table, "name"), True)
-        self.assertIs(sql.references_column(table, "weight"), True)
-        # Remove constraint.
-        with connection.schema_editor() as editor:
-            editor.remove_constraint(Author, constraint)
+            table = Author._meta.db_table
+            constraints = self.get_constraints(table)
+            self.assertIn(constraint.name, constraints)
+            self.assertIs(constraints[constraint.name]["unique"], True)
+            # SQL contains columns.
+            self.assertIs(sql.references_column(table, "name"), True)
+            self.assertIs(sql.references_column(table, "weight"), True)
+            # Remove constraint.
+            with connection.schema_editor() as editor:
+                editor.remove_constraint(Author, constraint)
+        name_field = Author._meta.get_field("name")
+        weight_field = Author._meta.get_field("weight")
+        self.assertIsNone(name_field.get_transform("lower"))
+        self.assertIsNone(weight_field.get_transform("abs"))
         self.assertNotIn(constraint.name, self.get_constraints(table))
 
     @skipUnlessDBFeature("supports_expression_indexes")