diff --git a/toolkit/identity/FirefoxAccounts.jsm b/toolkit/identity/FirefoxAccounts.jsm
index 8ba3817f85c..e8374480caa 100644
--- a/toolkit/identity/FirefoxAccounts.jsm
+++ b/toolkit/identity/FirefoxAccounts.jsm
@@ -187,7 +187,7 @@ FxAccountsService.prototype = {
       error => {
         log.error("get assertion failed: " + JSON.stringify(error));
         // Cancellation is passed through an error channel; here we reroute.
-        if (error.details && (error.details.error == "DIALOG_CLOSED_BY_USER")) {
+        if (error.error && (error.error.details == "DIALOG_CLOSED_BY_USER")) {
           return this.doCancel(aRPId);
         }
         this.doError(aRPId, error);