diff --git a/demo/demo.jspp b/demo/demo.jspp
index cef6a69..538c609 100644
--- a/demo/demo.jspp
+++ b/demo/demo.jspp
@@ -218,31 +218,34 @@ Demo.prototype.doCommand = function() {
   this.gotoState(STATE_PROMPT);
   var tokens              = new Tokens(this.line);
   this.line               = '';
-  var cmd                 = tokens.nextToken().toUpperCase();
-  if (cmd.match(/^[0-9]+$/)) {
-    tokens.removeLineNumber();
-    var lineNumber        = parseInt(cmd);
-    var index             = this.findLine(lineNumber);
-    if (tokens.nextToken() == undefined) {
-      if (index > 0) {
-        // Delete line from program
-        this.program.splice(index, 1);
+  var cmd                 = tokens.nextToken();
+  if (cmd != undefined) {
+    cmd                   = cmd.toUpperCase();
+    if (cmd.match(/^[0-9]+$/)) {
+      tokens.removeLineNumber();
+      var lineNumber        = parseInt(cmd);
+      var index             = this.findLine(lineNumber);
+      if (tokens.nextToken() == undefined) {
+        if (index > 0) {
+          // Delete line from program
+          this.program.splice(index, 1);
+        }
+      } else {
+        if (index >= 0) {
+          // Replace line in program
+          this.program[index].setTokens(tokens);
+        } else {
+          // Add new line to program
+          this.program.splice(-index - 1, 0, new Line(lineNumber, tokens));
+        }
       }
     } else {
-      if (index >= 0) {
-        // Replace line in program
-        this.program[index].setTokens(tokens);
-      } else {
-        // Add new line to program
-        this.program.splice(-index - 1, 0, new Line(lineNumber, tokens));
-      }
+      this.currentLineIndex = -1;
+      this.tokens           = tokens;
+      this.gotoState(STATE_EVAL);
     }
-  } else {
-    this.currentLineIndex = -1;
-    this.tokens           = tokens;
-    this.gotoState(STATE_EVAL);
+    tokens.reset();
   }
-  tokens.reset();
 };
 
 Demo.prototype.doEval = function() {