diff --git a/Libraries/Promise.js b/Libraries/Promise.js
index 7b52e135cc33f9..6fea6d0c38cd2e 100644
--- a/Libraries/Promise.js
+++ b/Libraries/Promise.js
@@ -18,6 +18,9 @@ if (__DEV__) {
     allRejections: true,
     onUnhandled: (id, error = {}) => {
       const {message = null, stack = null} = error;
+      if (typeof error === 'string' || error instanceof String) {
+        message = error;
+      }
       const warning =
         `Possible Unhandled Promise Rejection (id: ${id}):\n` +
         (message == null ? '' : `${message}\n`) +