diff --git a/packages/scheduler/src/SchedulerFeatureFlags.js b/packages/scheduler/src/SchedulerFeatureFlags.js
index 98cf4bad14d7..7e17741524a4 100644
--- a/packages/scheduler/src/SchedulerFeatureFlags.js
+++ b/packages/scheduler/src/SchedulerFeatureFlags.js
@@ -10,5 +10,5 @@ export const enableSchedulerDebugging = false;
 export const enableIsInputPending = false;
 export const requestIdleCallbackBeforeFirstFrame = false;
 export const requestTimerEventBeforeFirstFrame = false;
-export const enableMessageLoopImplementation = false;
+export const enableMessageLoopImplementation = true;
 export const enableProfiling = __PROFILE__;
diff --git a/packages/scheduler/src/__tests__/SchedulerDOM-test.js b/packages/scheduler/src/__tests__/SchedulerRAFOld-test.internal.js
similarity index 99%
rename from packages/scheduler/src/__tests__/SchedulerDOM-test.js
rename to packages/scheduler/src/__tests__/SchedulerRAFOld-test.internal.js
index dacfb53e9eb7..04e73a4e355f 100644
--- a/packages/scheduler/src/__tests__/SchedulerDOM-test.js
+++ b/packages/scheduler/src/__tests__/SchedulerRAFOld-test.internal.js
@@ -16,7 +16,9 @@ type FrameTimeoutConfigType = {
   timePastFrameDeadline: ?number,
 };
 
-describe('SchedulerDOM', () => {
+// Note: this is testing the implementation that we turned off.
+// enableMessageLoopImplementation is true on master.
+describe('SchedulerRAFOld', () => {
   let rAFCallbacks = [];
   let postMessageCallback;
   let postMessageEvents = [];
@@ -101,6 +103,7 @@ describe('SchedulerDOM', () => {
       ),
     );
 
+    require('scheduler/src/SchedulerFeatureFlags').enableMessageLoopImplementation = false;
     Scheduler = require('scheduler');
   });
 
diff --git a/packages/scheduler/src/forks/SchedulerFeatureFlags.www.js b/packages/scheduler/src/forks/SchedulerFeatureFlags.www.js
index 360be98e603f..f4bebebf2c29 100644
--- a/packages/scheduler/src/forks/SchedulerFeatureFlags.www.js
+++ b/packages/scheduler/src/forks/SchedulerFeatureFlags.www.js
@@ -9,9 +9,9 @@
 export const {
   enableIsInputPending,
   enableSchedulerDebugging,
-  requestIdleCallbackBeforeFirstFrame,
-  requestTimerEventBeforeFirstFrame,
-  enableMessageLoopImplementation,
 } = require('SchedulerFeatureFlags');
 
 export const enableProfiling = __PROFILE__;
+export const requestIdleCallbackBeforeFirstFrame = false;
+export const requestTimerEventBeforeFirstFrame = false;
+export const enableMessageLoopImplementation = true;