diff --git a/lib/http/server.js b/lib/http/server.js
index c3229c37..510ca5b3 100644
--- a/lib/http/server.js
+++ b/lib/http/server.js
@@ -214,7 +214,7 @@ HTTPServer.prototype._init = function _init() {
 
     if (params.start != null) {
       options.start = Number(params.start);
-      assert(utils.isUInt32(options.height), 'Start must be a number.');
+      assert(utils.isUInt32(options.start), 'Start must be a number.');
     }
 
     if (params.end != null) {