diff --git a/src/BackgroundTokenizer.js b/src/BackgroundTokenizer.js
index ff681786..d9cfe1f6 100644
--- a/src/BackgroundTokenizer.js
+++ b/src/BackgroundTokenizer.js
@@ -22,8 +22,7 @@ ace.BackgroundTokenizer = function(tokenizer) {
 
             var state = self.currentLine == 0 ? "start"
                     : self.lines[self.currentLine - 1].state;
-            self.lines[self.currentLine] = self.tokenizer.getLineTokens(line,
-                                                                        state);
+            self.lines[self.currentLine] = self.tokenizer.getLineTokens(line, state);
 
             // only check every 30 lines
             processedLines += 1;
@@ -69,11 +68,12 @@ ace.BackgroundTokenizer.prototype.fireUpdateEvent = function(firstRow, lastRow)
 ace.BackgroundTokenizer.prototype.start = function(startRow) {
     this.currentLine = Math.min(startRow || 0, this.currentLine,
                                 this.textLines.length);
-    this.lines.splice(startRow, this.lines.length);
+
+    this.lines.splice(this.currentLine, this.lines.length);
 
     if (!this.running) {
-        this.running = true;
-        setTimeout(this._worker, 50);
+        clearTimeout(this.running);
+        this.running = setTimeout(this._worker, 50);
     }
 };
 
diff --git a/src/Editor.js b/src/Editor.js
index 72ef38a3..b286d150 100644
--- a/src/Editor.js
+++ b/src/Editor.js
@@ -129,8 +129,8 @@ ace.Editor.prototype.onBlur = function() {
 
 ace.Editor.prototype.onDocumentChange = function(e) {
     var data = e.data;
-    this.bgTokenizer.start(data.startRow);
-    this.renderer.updateLines(data.startRow, data.endRow);
+    this.bgTokenizer.start(data.firstRow);
+    this.renderer.updateLines(data.firstRow, data.endRow);
 };
 
 ace.Editor.prototype.onTokenizerUpdate = function(e) {