diff --git a/lib/UnexpectedError.js b/lib/UnexpectedError.js
index 626079eb3..72232a3f1 100644
--- a/lib/UnexpectedError.js
+++ b/lib/UnexpectedError.js
@@ -9,6 +9,8 @@ function UnexpectedError(expect, assertion, parent) {
     if (Error.captureStackTrace) {
         Error.captureStackTrace(this, UnexpectedError);
     } else {
+        // Throw the error to make sure it has its stack serialized:
+        try { throw base; } catch (err) {}
         this.stack = base.stack;
     }