diff --git a/js/kiri-driver-fdm.js b/js/kiri-driver-fdm.js
index 1f123ca5..6dab0ad0 100644
--- a/js/kiri-driver-fdm.js
+++ b/js/kiri-driver-fdm.js
@@ -338,9 +338,11 @@ var gs_kiri_fdm = exports;
         for (var i=0; i<device.gcodePre.length; i++) {
             var line = device.gcodePre[i];
             if (device.extrudeAbs && line.indexOf('E') > 0) {
-                line.split(' ').forEach(function (tok) {
+                line.split(";")[0].split(' ').forEach(function (tok) {
                     // use max E position from gcode-preamble
-                    if (tok[0] == 'E') outputLength = Math.max(outputLength, parseFloat(tok.substring(1)));
+                    if (tok[0] == 'E') {
+                        outputLength = Math.max(outputLength, parseFloat(tok.substring(1)) || 0);
+                    }
                 });
             }
             append(constReplace(line, consts));