diff --git a/chrome/browser/reduce_accept_language/reduce_accept_language_browsertest.cc b/chrome/browser/reduce_accept_language/reduce_accept_language_browsertest.cc
index 15fa72a1a64e5..9807382cb23fe 100644
--- a/chrome/browser/reduce_accept_language/reduce_accept_language_browsertest.cc
+++ b/chrome/browser/reduce_accept_language/reduce_accept_language_browsertest.cc
@@ -531,9 +531,9 @@ class ReduceAcceptLanguageBrowserTest : public policy::PolicyTest {
 class DisableFeatureReduceAcceptLanguageBrowserTest
     : public ReduceAcceptLanguageBrowserTest {
   void EnabledFeatures() override {
-    std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
-    feature_list->InitFromCommandLine("", "ReduceAcceptLanguage");
-    scoped_feature_list_.InitWithFeatureList(std::move(feature_list));
+    scoped_feature_list_.InitWithFeatures(
+        {}, {network::features::kReduceAcceptLanguage,
+             network::features::kReduceAcceptLanguageHTTP});
   }
 };
 
diff --git a/content/browser/web_package/signed_exchange_request_handler_browsertest.cc b/content/browser/web_package/signed_exchange_request_handler_browsertest.cc
index 18910b797e8a2..d10eeb5975c47 100644
--- a/content/browser/web_package/signed_exchange_request_handler_browsertest.cc
+++ b/content/browser/web_package/signed_exchange_request_handler_browsertest.cc
@@ -265,7 +265,8 @@ class SignedExchangeRequestHandlerBrowserTest
     // TODO(crbug.com/334954143) Fix the AcceptLanguage tests when turning on
     // the ReduceAcceptLanguage feature.
     scoped_feature_list_.InitWithFeatures(
-        {}, {network::features::kReduceAcceptLanguage});
+        {}, {network::features::kReduceAcceptLanguage,
+             network::features::kReduceAcceptLanguageHTTP});
     use_prefetch_ = GetParam();
   }
 
diff --git a/testing/variations/fieldtrial_testing_config.json b/testing/variations/fieldtrial_testing_config.json
index 357e9fdcf9d27..e43a854f95c86 100644
--- a/testing/variations/fieldtrial_testing_config.json
+++ b/testing/variations/fieldtrial_testing_config.json
@@ -19618,6 +19618,25 @@
             ]
         }
     ],
+    "ReduceAcceptLanguageHTTP": [
+        {
+            "platforms": [
+                "android",
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "ReduceAcceptLanguageHTTP"
+                    ]
+                }
+            ]
+        }
+    ],
     "ReduceCpuUtilization2": [
         {
             "platforms": [