diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index f3aade3916..35b82dc1e5 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -5,7 +5,7 @@ from datetime import datetime
 from django.db.backends.ddl_references import (
     Columns, ForeignKeyName, IndexName, Statement, Table,
 )
-from django.db.backends.utils import strip_quotes
+from django.db.backends.utils import split_identifier
 from django.db.models import Index
 from django.db.transaction import TransactionManagementError, atomic
 from django.utils import timezone
@@ -858,7 +858,7 @@ class BaseDatabaseSchemaEditor:
         The name is divided into 3 parts: the table name, the column names,
         and a unique digest and suffix.
         """
-        table_name = strip_quotes(table_name)
+        _, table_name = split_identifier(table_name)
         hash_data = [table_name] + list(column_names)
         hash_suffix_part = '%s%s' % (self._digest(*hash_data), suffix)
         max_length = self.connection.ops.max_name_length() or 200
diff --git a/django/db/backends/utils.py b/django/db/backends/utils.py
index 816164d36a..f4641e3db8 100644
--- a/django/db/backends/utils.py
+++ b/django/db/backends/utils.py
@@ -3,7 +3,6 @@ import decimal
 import functools
 import hashlib
 import logging
-import re
 from time import time
 
 from django.conf import settings
@@ -194,20 +193,35 @@ def rev_typecast_decimal(d):
     return str(d)
 
 
-def truncate_name(name, length=None, hash_len=4):
+def split_identifier(identifier):
     """
-    Shorten a string to a repeatable mangled version with the given length.
-    If a quote stripped name contains a username, e.g. USERNAME"."TABLE,
+    Split a SQL identifier into a two element tuple of (namespace, name).
+
+    The identifier could be a table, column, or sequence name might be prefixed
+    by a namespace.
+    """
+    try:
+        namespace, name = identifier.split('"."')
+    except ValueError:
+        namespace, name = '', identifier
+    return namespace.strip('"'), name.strip('"')
+
+
+def truncate_name(identifier, length=None, hash_len=4):
+    """
+    Shorten a SQL identifier to a repeatable mangled version with the given
+    length.
+
+    If a quote stripped name contains a namespace, e.g. USERNAME"."TABLE,
     truncate the table portion only.
     """
-    match = re.match(r'([^"]+)"\."([^"]+)', name)
-    table_name = match.group(2) if match else name
+    namespace, name = split_identifier(identifier)
 
-    if length is None or len(table_name) <= length:
-        return name
+    if length is None or len(name) <= length:
+        return identifier
 
-    hsh = hashlib.md5(force_bytes(table_name)).hexdigest()[:hash_len]
-    return '%s%s%s' % (match.group(1) + '"."' if match else '', table_name[:length - hash_len], hsh)
+    digest = hashlib.md5(force_bytes(name)).hexdigest()[:hash_len]
+    return '%s%s%s' % ('%s"."' % namespace if namespace else '', name[:length - hash_len], digest)
 
 
 def format_number(value, max_digits, decimal_places):
diff --git a/docs/releases/1.11.8.txt b/docs/releases/1.11.8.txt
index 7e4963f713..426b6d92b2 100644
--- a/docs/releases/1.11.8.txt
+++ b/docs/releases/1.11.8.txt
@@ -15,3 +15,6 @@ Bugfixes
 * Added support for ``QuerySet.values()`` and ``values_list()`` for
   ``union()``, ``difference()``, and ``intersection()`` queries
   (:ticket:`28781`).
+
+* Fixed incorrect index name truncation when using a namespaced ``db_table``
+  (:ticket:`28792`).
diff --git a/tests/backends/test_utils.py b/tests/backends/test_utils.py
index be9aeaf698..cd4911fd1a 100644
--- a/tests/backends/test_utils.py
+++ b/tests/backends/test_utils.py
@@ -2,7 +2,9 @@
 from decimal import Decimal, Rounded
 
 from django.db import connection
-from django.db.backends.utils import format_number, truncate_name
+from django.db.backends.utils import (
+    format_number, split_identifier, truncate_name,
+)
 from django.db.utils import NotSupportedError
 from django.test import (
     SimpleTestCase, TransactionTestCase, skipIfDBFeature, skipUnlessDBFeature,
@@ -21,6 +23,12 @@ class TestUtils(SimpleTestCase):
         self.assertEqual(truncate_name('username"."some_long_table', 10), 'username"."some_la38a')
         self.assertEqual(truncate_name('username"."some_long_table', 10, 3), 'username"."some_loa38')
 
+    def test_split_identifier(self):
+        self.assertEqual(split_identifier('some_table'), ('', 'some_table'))
+        self.assertEqual(split_identifier('"some_table"'), ('', 'some_table'))
+        self.assertEqual(split_identifier('namespace"."some_table'), ('namespace', 'some_table'))
+        self.assertEqual(split_identifier('"namespace"."some_table"'), ('namespace', 'some_table'))
+
     def test_format_number(self):
         def equal(value, max_d, places, result):
             self.assertEqual(format_number(Decimal(value), max_d, places), result)
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index f2a96294cc..66a54b1ce4 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -2370,6 +2370,21 @@ class SchemaTests(TransactionTestCase):
             cast_function=lambda x: x.time(),
         )
 
+    def test_namespaced_db_table_create_index_name(self):
+        """
+        Table names are stripped of their namespace/schema before being used to
+        generate index names.
+        """
+        with connection.schema_editor() as editor:
+            max_name_length = connection.ops.max_name_length() or 200
+            namespace = 'n' * max_name_length
+            table_name = 't' * max_name_length
+            namespaced_table_name = '"%s"."%s"' % (namespace, table_name)
+            self.assertEqual(
+                editor._create_index_name(table_name, []),
+                editor._create_index_name(namespaced_table_name, []),
+            )
+
     @unittest.skipUnless(connection.vendor == 'oracle', 'Oracle specific db_table syntax')
     def test_creation_with_db_table_double_quotes(self):
         oracle_user = connection.creation._test_database_user()