diff --git a/src/harness/harnessLanguageService.ts b/src/harness/harnessLanguageService.ts
index e850fb57c01..430dcc24477 100644
--- a/src/harness/harnessLanguageService.ts
+++ b/src/harness/harnessLanguageService.ts
@@ -126,7 +126,7 @@ module Harness.LanguageService {
             isOpen: boolean,
             textChangeRange: ts.TextChangeRange
             ): ts.SourceFile {
-            return ts.updateLanguageServiceSourceFile(document, scriptSnapshot, version, isOpen, textChangeRange, /*useIncremental:*/ false);
+            return ts.updateLanguageServiceSourceFile(document, scriptSnapshot, version, isOpen, textChangeRange);
         }
 
         public releaseDocument(fileName: string, compilationSettings: ts.CompilerOptions): void {
diff --git a/src/services/services.ts b/src/services/services.ts
index 0c3abf090ae..163b8d75ded 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -1519,7 +1519,7 @@ module ts {
                 var editRange = this.hostCache.getChangeRange(filename, this.currentFileVersion, this.currentSourceFile.scriptSnapshot);
 
                 var start = new Date().getTime();
-                sourceFile = updateLanguageServiceSourceFile(this.currentSourceFile, scriptSnapshot, version, /*isOpen*/ true, editRange, /*useIncremental:*/ false);
+                sourceFile = updateLanguageServiceSourceFile(this.currentSourceFile, scriptSnapshot, version, /*isOpen*/ true, editRange);
                 this.host.log("SyntaxTreeCache.Initialize: updateSourceFile: " + (new Date().getTime() - start));
             }
 
@@ -1553,7 +1553,9 @@ module ts {
         return sourceFile;
     }
 
-    export function updateLanguageServiceSourceFile(sourceFile: SourceFile, scriptSnapshot: IScriptSnapshot, version: string, isOpen: boolean, textChangeRange: TextChangeRange, useIncremental: boolean): SourceFile {
+    export var disableIncrementalParsing = false;
+
+    export function updateLanguageServiceSourceFile(sourceFile: SourceFile, scriptSnapshot: IScriptSnapshot, version: string, isOpen: boolean, textChangeRange: TextChangeRange): SourceFile {
         if (textChangeRange && Debug.shouldAssert(AssertionLevel.Normal)) {
             var oldText = sourceFile.scriptSnapshot;
             var newText = scriptSnapshot;
@@ -1576,7 +1578,7 @@ module ts {
         if (textChangeRange) {
             if (version !== sourceFile.version || isOpen != sourceFile.isOpen) {
                 // Once incremental parsing is ready, then just call into this function.
-                if (useIncremental) {
+                if (!disableIncrementalParsing) {
                     var newSourceFile = sourceFile.update(scriptSnapshot.getText(0, scriptSnapshot.getLength()), textChangeRange);
                     setSourceFileFields(newSourceFile, scriptSnapshot, version, isOpen);
                     return newSourceFile;
@@ -1663,7 +1665,7 @@ module ts {
             var entry = lookUp(bucket, filename);
             Debug.assert(entry !== undefined);
 
-            entry.sourceFile = updateLanguageServiceSourceFile(entry.sourceFile, scriptSnapshot, version, isOpen, textChangeRange, /*useIncremental:*/ false);
+            entry.sourceFile = updateLanguageServiceSourceFile(entry.sourceFile, scriptSnapshot, version, isOpen, textChangeRange);
             return entry.sourceFile;
         }
 
diff --git a/tests/cases/unittests/incrementalParser.ts b/tests/cases/unittests/incrementalParser.ts
index a236776a45d..263c396842d 100644
--- a/tests/cases/unittests/incrementalParser.ts
+++ b/tests/cases/unittests/incrementalParser.ts
@@ -55,7 +55,7 @@ module ts {
         Utils.assertInvariants(newTree, /*parent:*/ undefined);
 
         // Create a tree for the new text, in an incremental fashion.
-        var incrementalNewTree = updateLanguageServiceSourceFile(oldTree, newText, oldTree.version + ".", /*isOpen:*/ true, textChangeRange, /*useIncremental:*/ true);
+        var incrementalNewTree = updateLanguageServiceSourceFile(oldTree, newText, oldTree.version + ".", /*isOpen:*/ true, textChangeRange);
         Utils.assertInvariants(incrementalNewTree, /*parent:*/ undefined);
 
         // We should get the same tree when doign a full or incremental parse.