diff --git a/packages/scheduler/src/SchedulerProfiling.js b/packages/scheduler/src/SchedulerProfiling.js
index 4972c6018e199..9170a844737d7 100644
--- a/packages/scheduler/src/SchedulerProfiling.js
+++ b/packages/scheduler/src/SchedulerProfiling.js
@@ -31,7 +31,7 @@ const TaskYieldEvent = 6;
 const SchedulerSuspendEvent = 7;
 const SchedulerResumeEvent = 8;
 
-function logEvent(entries) {
+function logEvent(entries: Array) {
   if (eventLog !== null) {
     const offset = eventLogIndex;
     eventLogIndex += entries.length;
diff --git a/packages/scheduler/src/forks/Scheduler.js b/packages/scheduler/src/forks/Scheduler.js
index 22c70f58486bf..27468f3db4cb7 100644
--- a/packages/scheduler/src/forks/Scheduler.js
+++ b/packages/scheduler/src/forks/Scheduler.js
@@ -637,7 +637,7 @@ function requestHostCallback(callback) {
   }
 }
 
-function requestHostTimeout(callback, ms) {
+function requestHostTimeout(callback, ms: number) {
   // $FlowFixMe[not-a-function] nullable value
   taskTimeoutID = localSetTimeout(() => {
     callback(getCurrentTime());
diff --git a/packages/scheduler/src/forks/SchedulerMock.js b/packages/scheduler/src/forks/SchedulerMock.js
index 389edcb699e35..8574f0ede9cda 100644
--- a/packages/scheduler/src/forks/SchedulerMock.js
+++ b/packages/scheduler/src/forks/SchedulerMock.js
@@ -191,7 +191,7 @@ function flushWork(hasTimeRemaining: boolean, initialTime: number) {
   }
 }
 
-function workLoop(hasTimeRemaining, initialTime: number): boolean {
+function workLoop(hasTimeRemaining: boolean, initialTime: number): boolean {
   let currentTime = initialTime;
   advanceTimers(currentTime);
   currentTask = peek(taskQueue);