diff --git a/vendor/clouds3d.js b/vendor/clouds3d.js
index 477806b..f7d3ae7 100644
--- a/vendor/clouds3d.js
+++ b/vendor/clouds3d.js
@@ -2848,6 +2848,7 @@ function buildCityVBO(gl) {
             verts.push(x, y, z, sz * (0.6 + 0.8 * h3), bri * (0.55 + 0.7 * h3));
         }
     }
+    var _bT = performance.now();
     if (cityVbo) gl.deleteBuffer(cityVbo);
     cityVbo = null; cityCount = 0;
     if (verts.length < 5) { sanitizeCityAttribSlots(gl); return; }
@@ -2856,7 +2857,8 @@ function buildCityVBO(gl) {
     gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(verts), gl.STATIC_DRAW);
     cityVbo = vbo; cityCount = verts.length / 5;
     // debug counter (also used by headless smoke tests)
-    window.__cityDbg = { places: cityGeo ? cityGeo.length : 0, lights: cityCount };
+    window.__cityDbg = { places: cityGeo ? cityGeo.length : 0, lights: cityCount,
+                         buildMs: +(performance.now() - _bT).toFixed(1) };
     sanitizeCityAttribSlots(gl);
     if (!cityProg) {
         cityProg = makeProgram(gl, CITY_VERT_SRC, CITY_FRAG_SRC);