diff --git a/matrix-util.js b/matrix-util.js
index e88b047..40d4773 100644
--- a/matrix-util.js
+++ b/matrix-util.js
@@ -123,7 +123,7 @@ MatrixUtil.prototype.isPartnerOffline = function(partner) {
     return true;
 }
 
-MatrixUtil.prototype._updateLastResponseTime(partner) {
+MatrixUtil.prototype._updateLastResponseTime = function(partner) {
     let matrix = this.matrix;
 
     if (!matrix.buddies[partner]['last_outgoing']) {