--- a/services/fxaccounts/FxAccountsClient.jsm
+++ b/services/fxaccounts/FxAccountsClient.jsm
@@ -182,17 +182,17 @@ this.FxAccountsClient.prototype = {
   signCertificate: function (sessionTokenHex, serializedPublicKey, lifetime) {
     let creds = this._deriveHawkCredentials(sessionTokenHex, "sessionToken");
 
     let body = { publicKey: serializedPublicKey,
                  duration: lifetime };
     return Promise.resolve()
       .then(_ => this._request("/certificate/sign", "POST", creds, body))
       .then(resp => resp.cert,
-            err => {dump("HAWK.signCertificate error: " + err + "\n");
+            err => {dump("HAWK.signCertificate error: " + JSON.stringify(err) + "\n");
                     throw err;});
   },
 
   /**
    * Determine if an account exists
    *
    * @param email
    *        The email address to check