diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index 8002b019551..5fbf7d976ff 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -796,9 +796,15 @@ module Harness {
             }
         }
 
+        export function createSourceFileAndAssertInvariants(fileName: string, sourceText: string, languageVersion: ts.ScriptTarget) {
+            var result = ts.createSourceFile(fileName, sourceText, languageVersion, /*setParentNodes:*/ true);
+            Utils.assertInvariants(result, /*parent:*/ undefined);
+            return result;
+        }
+
         export var defaultLibFileName = 'lib.d.ts';
-        export var defaultLibSourceFile = ts.createSourceFile(defaultLibFileName, IO.readFile(libFolder + 'lib.core.d.ts'), /*languageVersion*/ ts.ScriptTarget.Latest);
-        export var defaultES6LibSourceFile = ts.createSourceFile(defaultLibFileName, IO.readFile(libFolder + 'lib.core.es6.d.ts'), /*languageVersion*/ ts.ScriptTarget.Latest);
+        export var defaultLibSourceFile = createSourceFileAndAssertInvariants(defaultLibFileName, IO.readFile(libFolder + 'lib.core.d.ts'), /*languageVersion*/ ts.ScriptTarget.Latest);
+        export var defaultES6LibSourceFile = createSourceFileAndAssertInvariants(defaultLibFileName, IO.readFile(libFolder + 'lib.core.es6.d.ts'), /*languageVersion*/ ts.ScriptTarget.Latest);
 
 
         // Cache these between executions so we don't have to re-parse them for every test
@@ -828,7 +834,7 @@ module Harness {
             function register(file: { unitName: string; content: string; }) {
                 if (file.content !== undefined) {
                     var fileName = ts.normalizeSlashes(file.unitName);
-                    filemap[getCanonicalFileName(fileName)] = ts.createSourceFile(fileName, file.content, scriptTarget);
+                    filemap[getCanonicalFileName(fileName)] = createSourceFileAndAssertInvariants(fileName, file.content, scriptTarget);
                 }
             };
             inputFiles.forEach(register);
@@ -845,7 +851,7 @@ module Harness {
                     }
                     else if (fn === fourslashFileName) {
                         var tsFn = 'tests/cases/fourslash/' + fourslashFileName;
-                        fourslashSourceFile = fourslashSourceFile || ts.createSourceFile(tsFn, Harness.IO.readFile(tsFn), scriptTarget);
+                        fourslashSourceFile = fourslashSourceFile || createSourceFileAndAssertInvariants(tsFn, Harness.IO.readFile(tsFn), scriptTarget);
                         return fourslashSourceFile;
                     }
                     else {
@@ -1069,7 +1075,7 @@ module Harness {
                 var register = (file: { unitName: string; content: string; }) => {
                     if (file.content !== undefined) {
                         var fileName = ts.normalizeSlashes(file.unitName);
-                        filemap[getCanonicalFileName(fileName)] = ts.createSourceFile(fileName, file.content, options.target);
+                        filemap[getCanonicalFileName(fileName)] = createSourceFileAndAssertInvariants(fileName, file.content, options.target);
                     }
                 };
                 inputFiles.forEach(register);
diff --git a/src/harness/harnessLanguageService.ts b/src/harness/harnessLanguageService.ts
index 547f8ccce48..bf9c75a7167 100644
--- a/src/harness/harnessLanguageService.ts
+++ b/src/harness/harnessLanguageService.ts
@@ -102,7 +102,7 @@ module Harness.LanguageService {
             compilationSettings: ts.CompilerOptions,
             scriptSnapshot: ts.IScriptSnapshot,
             version: string): ts.SourceFile {
-            var sourceFile = ts.createSourceFile(fileName, scriptSnapshot.getText(0, scriptSnapshot.getLength()), compilationSettings.target);
+            var sourceFile = Compiler.createSourceFileAndAssertInvariants(fileName, scriptSnapshot.getText(0, scriptSnapshot.getLength()), compilationSettings.target);
             sourceFile.version = version;
             return sourceFile;
         }
@@ -115,7 +115,9 @@ module Harness.LanguageService {
             version: string,
             textChangeRange: ts.TextChangeRange
             ): ts.SourceFile {
-            return ts.updateLanguageServiceSourceFile(document, scriptSnapshot, version, textChangeRange);
+            var result = ts.updateLanguageServiceSourceFile(document, scriptSnapshot, version, textChangeRange);
+            Utils.assertInvariants(result, /*parent:*/ undefined);
+            return result;
         }
 
         public releaseDocument(fileName: string, compilationSettings: ts.CompilerOptions): void {
@@ -269,7 +271,7 @@ module Harness.LanguageService {
 
         /** Parse file given its source text */
         public parseSourceText(fileName: string, sourceText: ts.IScriptSnapshot): ts.SourceFile {
-            var result = ts.createSourceFile(fileName, sourceText.getText(0, sourceText.getLength()), ts.ScriptTarget.Latest);
+            var result = Compiler.createSourceFileAndAssertInvariants(fileName, sourceText.getText(0, sourceText.getLength()), ts.ScriptTarget.Latest);
             result.version = "1";
             return result;
         }
diff --git a/src/harness/projectsRunner.ts b/src/harness/projectsRunner.ts
index 0fde9a9d77c..3291128a7a5 100644
--- a/src/harness/projectsRunner.ts
+++ b/src/harness/projectsRunner.ts
@@ -172,7 +172,7 @@ class ProjectRunner extends RunnerBase {
                 else {
                     var text = getSourceFileText(fileName);
                     if (text !== undefined) {
-                        sourceFile = ts.createSourceFile(fileName, text, languageVersion);
+                        sourceFile = Harness.Compiler.createSourceFileAndAssertInvariants(fileName, text, languageVersion);
                     }
                 }