diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index 7e22f879ba..4c89231295 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -282,7 +282,7 @@ class BaseDatabaseFeatures:
     # Does the backend support covering indexes (CREATE INDEX ... INCLUDE ...)?
     supports_covering_indexes = False
     # Does the backend support indexes on expressions?
-    supports_expression_indexes = False
+    supports_expression_indexes = True
     # Does the backend treat COLLATE as an indexed expression?
     collate_as_index_expression = False
 
diff --git a/django/db/backends/oracle/features.py b/django/db/backends/oracle/features.py
index bedc398517..2570675809 100644
--- a/django/db/backends/oracle/features.py
+++ b/django/db/backends/oracle/features.py
@@ -59,7 +59,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_ignore_conflicts = False
     max_query_params = 2**16 - 1
     supports_partial_indexes = False
-    supports_expression_indexes = True
     supports_slicing_ordering_in_compound = True
     allows_multiple_constraints_on_same_fields = False
     supports_boolean_expr_in_select_clause = False
diff --git a/django/db/backends/postgresql/features.py b/django/db/backends/postgresql/features.py
index b7ec377739..84259c0c19 100644
--- a/django/db/backends/postgresql/features.py
+++ b/django/db/backends/postgresql/features.py
@@ -58,7 +58,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_deferrable_unique_constraints = True
     has_json_operators = True
     json_key_contains_list_matching_requires_list = True
-    supports_expression_indexes = True
 
     django_test_skips = {
         'opclasses are PostgreSQL only.': {
diff --git a/django/db/backends/sqlite3/features.py b/django/db/backends/sqlite3/features.py
index 31055f8f99..3348256c74 100644
--- a/django/db/backends/sqlite3/features.py
+++ b/django/db/backends/sqlite3/features.py
@@ -38,7 +38,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_pragma_foreign_key_check = Database.sqlite_version_info >= (3, 20, 0)
     can_defer_constraint_checks = supports_pragma_foreign_key_check
     supports_functions_in_partial_indexes = Database.sqlite_version_info >= (3, 15, 0)
-    supports_expression_indexes = True
     supports_over_clause = Database.sqlite_version_info >= (3, 25, 0)
     supports_frame_range_fixed_distance = Database.sqlite_version_info >= (3, 28, 0)
     supports_aggregate_filter_clause = Database.sqlite_version_info >= (3, 30, 1)
diff --git a/docs/releases/3.2.txt b/docs/releases/3.2.txt
index 2b0f0ee6ee..3b1463be6f 100644
--- a/docs/releases/3.2.txt
+++ b/docs/releases/3.2.txt
@@ -668,6 +668,12 @@ backends.
   backends must implement ``DatabaseClient.settings_to_cmd_args_env()`` or
   override ``DatabaseClient.runshell()``.
 
+* Third-party database backends must implement support for functional indexes
+  (:attr:`.Index.expressions`) or set
+  ``DatabaseFeatures.supports_expression_indexes`` to ``False``. If ``COLLATE``
+  is not a part of the ``CREATE INDEX`` statement, set
+  ``DatabaseFeatures.collate_as_index_expression`` to ``True``.
+
 :mod:`django.contrib.admin`
 ---------------------------