diff --git a/HISTORY.md b/HISTORY.md
index e6dcfc17..a3406bb5 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -23,6 +23,7 @@
 * Some micro-optimizations for request matching
 
 **Bugfixes:**
+* Fix regression bug causing headers used for cache key to not guarantee sort order
 * Handle some additional corner cases when normalizing request data
 * Add support for `BaseCache` keyword arguments passed along with a backend instance
 * Fix issue with cache headers not being used correctly if `cache_control=True` is used with an `expire_after` value
diff --git a/requests_cache/cache_keys.py b/requests_cache/cache_keys.py
index d2a92cff..7029c7fc 100644
--- a/requests_cache/cache_keys.py
+++ b/requests_cache/cache_keys.py
@@ -81,7 +81,9 @@ def get_matched_headers(
     else:
         included = set(headers) - DEFAULT_EXCLUDE_HEADERS
 
-    return [f'{k.lower()}={headers[k]}' for k in included if k in headers]
+    return [
+        f'{k.lower()}={headers[k]}' for k in sorted(included, key=lambda x: x.lower()) if k in headers
+    ]
 
 
 def normalize_request(request: AnyRequest, ignored_parameters: ParamList) -> AnyPreparedRequest: