diff --git a/django/http/response.py b/django/http/response.py
index 929129342f..ab7158f7e0 100644
--- a/django/http/response.py
+++ b/django/http/response.py
@@ -5,7 +5,6 @@ import os
 import re
 import sys
 import time
-from collections.abc import Mapping
 from email.header import Header
 from http.client import responses
 from urllib.parse import quote, urlparse
@@ -16,9 +15,7 @@ from django.core.exceptions import DisallowedRedirect
 from django.core.serializers.json import DjangoJSONEncoder
 from django.http.cookie import SimpleCookie
 from django.utils import timezone
-from django.utils.datastructures import (
-    CaseInsensitiveMapping, _destruct_iterable_mapping_values,
-)
+from django.utils.datastructures import CaseInsensitiveMapping
 from django.utils.encoding import iri_to_uri
 from django.utils.http import http_date
 from django.utils.regex_helper import _lazy_re_compile
@@ -32,10 +29,8 @@ class ResponseHeaders(CaseInsensitiveMapping):
         Populate the initial data using __setitem__ to ensure values are
         correctly encoded.
         """
-        if not isinstance(data, Mapping):
-            data = {k: v for k, v in _destruct_iterable_mapping_values(data)}
         self._store = {}
-        for header, value in data.items():
+        for header, value in self._unpack_items(data):
             self[header] = value
 
     def _convert_to_charset(self, value, charset, mime_encode=False):
diff --git a/django/utils/datastructures.py b/django/utils/datastructures.py
index f1e9986ca1..18c91aa5e8 100644
--- a/django/utils/datastructures.py
+++ b/django/utils/datastructures.py
@@ -284,18 +284,6 @@ class DictWrapper(dict):
         return value
 
 
-def _destruct_iterable_mapping_values(data):
-    for i, elem in enumerate(data):
-        if len(elem) != 2:
-            raise ValueError(
-                'dictionary update sequence element #{} has '
-                'length {}; 2 is required.'.format(i, len(elem))
-            )
-        if not isinstance(elem[0], str):
-            raise ValueError('Element key %r invalid, only strings are allowed' % elem[0])
-        yield tuple(elem)
-
-
 class CaseInsensitiveMapping(Mapping):
     """
     Mapping allowing case-insensitive key lookups. Original case of keys is
@@ -315,9 +303,7 @@ class CaseInsensitiveMapping(Mapping):
     """
 
     def __init__(self, data):
-        if not isinstance(data, Mapping):
-            data = {k: v for k, v in _destruct_iterable_mapping_values(data)}
-        self._store = {k.lower(): (k, v) for k, v in data.items()}
+        self._store = {k.lower(): (k, v) for k, v in self._unpack_items(data)}
 
     def __getitem__(self, key):
         return self._store[key.lower()][1]
@@ -340,3 +326,20 @@ class CaseInsensitiveMapping(Mapping):
 
     def copy(self):
         return self
+
+    @staticmethod
+    def _unpack_items(data):
+        if isinstance(data, Mapping):
+            yield from data.items()
+            return
+        for i, elem in enumerate(data):
+            if len(elem) != 2:
+                raise ValueError(
+                    'dictionary update sequence element #{} has length {}; '
+                    '2 is required.'.format(i, len(elem))
+                )
+            if not isinstance(elem[0], str):
+                raise ValueError(
+                    'Element key %r invalid, only strings are allowed' % elem[0]
+                )
+            yield elem