diff --git a/lib/internal/process/promises.js b/lib/internal/process/promises.js
index 7710bfaf5f118f..82f15f9f9df51e 100644
--- a/lib/internal/process/promises.js
+++ b/lib/internal/process/promises.js
@@ -1,5 +1,7 @@
 'use strict';
 
+const { safeToString } = process.binding('util');
+
 const promiseRejectEvent = process._promiseRejectEvent;
 const hasBeenNotifiedProperty = new WeakMap();
 const promiseToGuidProperty = new WeakMap();
@@ -62,7 +64,9 @@ function setupPromises(scheduleMicrotasks) {
       if (reason instanceof Error) {
         process.emitWarning(reason.stack, 'UnhandledPromiseRejectionWarning');
       } else {
-        process.emitWarning(reason, 'UnhandledPromiseRejectionWarning');
+        process.emitWarning(
+          safeToString(reason), 'UnhandledPromiseRejectionWarning'
+        );
       }
     } catch (e) {
       // ignored