1 files changed, 1 insertions, 1 deletions
diff --git a/src/timer.ts b/src/timer.ts
index 9439b7199..ea7d34470 100644
--- a/src/timer.ts
+++ b/src/timer.ts
@@ -49,7 +49,7 @@ class TimeoutHandle {
 /**
  * Get a performance counter in milliseconds.
  */
-export let performanceNow = (() => {
+export const performanceNow: () => number = (() => {
   if (typeof process !== "undefined" && process.hrtime) {
     return () => {
       const t = process.hrtime();