diff --git a/packages/scheduler/src/forks/Scheduler.js b/packages/scheduler/src/forks/Scheduler.js
index 22c70f58486bf..3c6cacbdea920 100644
--- a/packages/scheduler/src/forks/Scheduler.js
+++ b/packages/scheduler/src/forks/Scheduler.js
@@ -85,8 +85,8 @@ var LOW_PRIORITY_TIMEOUT = 10000;
 var IDLE_PRIORITY_TIMEOUT = maxSigned31BitInt;
 
 // Tasks are stored on a min heap
-var taskQueue = [];
-var timerQueue = [];
+var taskQueue: Array<Task> = [];
+var timerQueue: Array<Task> = [];
 
 // Incrementing id counter. Used to maintain insertion order.
 var taskIdCounter = 1;
@@ -121,7 +121,7 @@ const isInputPending =
 
 const continuousOptions = {includeContinuous: enableIsInputPendingContinuous};
 
-function advanceTimers(currentTime) {
+function advanceTimers(currentTime: number) {
   // Check for tasks that are no longer delayed and add them to the queue.
   let timer = peek(timerQueue);
   while (timer !== null) {
@@ -145,7 +145,7 @@ function advanceTimers(currentTime) {
   }
 }
 
-function handleTimeout(currentTime) {
+function handleTimeout(currentTime: number) {
   isHostTimeoutScheduled = false;
   advanceTimers(currentTime);
 
@@ -162,7 +162,7 @@ function handleTimeout(currentTime) {
   }
 }
 
-function flushWork(hasTimeRemaining, initialTime) {
+function flushWork(hasTimeRemaining: boolean, initialTime: number) {
   if (enableProfiling) {
     markSchedulerUnsuspended(initialTime);
   }
@@ -206,7 +206,7 @@ function flushWork(hasTimeRemaining, initialTime) {
   }
 }
 
-function workLoop(hasTimeRemaining, initialTime) {
+function workLoop(hasTimeRemaining: boolean, initialTime: number) {
   let currentTime = initialTime;
   advanceTimers(currentTime);
   currentTask = peek(taskQueue);