diff --git a/src/harness/fourslash.ts b/src/harness/fourslash.ts
index 7f5f3688817..18d34e94b03 100644
--- a/src/harness/fourslash.ts
+++ b/src/harness/fourslash.ts
@@ -1434,6 +1434,13 @@ module FourSlash {
                 this.raiseError('Mismatched incremental/reference syntactic diagnostics for file ' + this.activeFile.fileName + '.\n=== Incremental diagnostics ===\n' + incrementalSyntaxDiagnostics + '\n=== Reference Diagnostics ===\n' + referenceSyntaxDiagnostics);
             }
 
+            var incrementalSourceFileJSON = Utils.sourceFileToJSON(incrementalSourceFile);
+            var referenceSourceFileJSON = Utils.sourceFileToJSON(referenceSourceFile);
+
+            if (incrementalSyntaxDiagnostics !== referenceSyntaxDiagnostics) {
+                this.raiseError('Mismatched incremental/reference ast for file ' + this.activeFile.fileName + '.\n=== Incremental AST ===\n' + incrementalSourceFileJSON + '\n=== Reference AST ===\n' + referenceSourceFileJSON);
+            }
+
              //if (this.editValidation !== IncrementalEditValidation.SyntacticOnly) {
              //   var compiler = new TypeScript.TypeScriptCompiler();
              //   for (var i = 0; i < this.testData.files.length; i++) {
diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index 095b0702b12..61e5fcbee65 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -189,6 +189,101 @@ module Utils {
             code: diagnostic.code
         };
     }
+
+    export function sourceFileToJSON(file: ts.SourceFile): string {
+        return JSON.stringify(file,(k, v) => {
+            return isNodeOrArray(v) ? serializeNode(v) : v;
+        }, "    ");
+
+        function getKindName(k: number): string {
+            return (<any>ts).SyntaxKind[k]
+        }
+
+        function getFlagName(flags: any, f: number): any {
+            if (f === 0) {
+                return 0;
+            }
+
+            var result = "";
+            ts.forEach(Object.getOwnPropertyNames(flags),(v: any) => {
+                if (isFinite(v)) {
+                    v = +v;
+                    if (f === +v) {
+                        result = flags[v];
+                        return true;
+                    }
+                    else if ((f & v) > 0) {
+                        if (result.length)
+                            result += " | ";
+                        result += flags[v];
+                        return false;
+                    }
+                }
+            });
+            return result;
+        }
+
+        function getNodeFlagName(f: number) { return getFlagName((<any>ts).NodeFlags, f); }
+        function getParserContextFlagName(f: number) { return getFlagName((<any>ts).ParserContextFlags, f); }
+
+        function serializeNode(n: ts.Node): any {
+            var o: any = { kind: getKindName(n.kind) };
+            o.containsParseError = ts.containsParseError(n);
+
+            ts.forEach(Object.getOwnPropertyNames(n), propertyName => {
+                switch (propertyName) {
+                    case "parent":
+                    case "symbol":
+                    case "locals":
+                    case "localSymbol":
+                    case "kind":
+                    case "semanticDiagnostics":
+                    case "id":
+                    case "nodeCount":
+                    case "symbolCount":
+                    case "identifierCount":
+                    case "scriptSnapshot":
+                        // Blacklist of items we never put in the baseline file.
+                        break;
+
+                    case "flags":
+                        // Print out flags with their enum names.
+                        o[propertyName] = getNodeFlagName(n.flags);
+                        break;
+
+                    case "parserContextFlags":
+                        o[propertyName] = getParserContextFlagName(n.parserContextFlags);
+                        break;
+
+                    case "referenceDiagnostics":
+                    case "parseDiagnostics":
+                    case "grammarDiagnostics":
+                        o[propertyName] = Utils.convertDiagnostics((<any>n)[propertyName]);
+                        break;
+
+                    case "nextContainer":
+                        if (n.nextContainer) {
+                            o[propertyName] = { kind: n.nextContainer.kind, pos: n.nextContainer.pos, end: n.nextContainer.end };
+                        }
+                        break;
+
+                    case "text":
+                        // Include 'text' field for identifiers/literals, but not for source files.
+                        if (n.kind !== ts.SyntaxKind.SourceFile) {
+                            o[propertyName] = (<any>n)[propertyName];
+                        }
+                        break;
+
+                    default:
+                        o[propertyName] = (<any>n)[propertyName];
+                }
+
+                return undefined;
+            });
+
+            return o;
+        }
+    }
 }
 
 module Harness.Path {
diff --git a/src/harness/test262Runner.ts b/src/harness/test262Runner.ts
index f6ba448015b..7e5bafde228 100644
--- a/src/harness/test262Runner.ts
+++ b/src/harness/test262Runner.ts
@@ -21,104 +21,6 @@ class Test262BaselineRunner extends RunnerBase {
         return Test262BaselineRunner.basePath + "/" + filename;
     }
 
-    private static serializeSourceFile(file: ts.SourceFile): string {
-        function getKindName(k: number): string {
-            return (<any>ts).SyntaxKind[k]
-        }
-
-        function getFlagName(flags: any, f: number): any {
-            if (f === 0) {
-                return 0;
-            }
-
-            var result = "";
-            ts.forEach(Object.getOwnPropertyNames(flags), (v: any) => {
-                if (isFinite(v)) {
-                    v = +v;
-                    if (f === +v) {
-                        result = flags[v];
-                        return true;
-                    }
-                    else if ((f & v) > 0) {
-                        if (result.length)
-                            result += " | ";
-                        result += flags[v];
-                        return false;
-                    }
-                }
-            });
-            return result;
-        }
-
-        function getNodeFlagName(f: number) { return getFlagName((<any>ts).NodeFlags, f); }
-        function getParserContextFlagName(f: number) { return getFlagName((<any>ts).ParserContextFlags, f); }
-
-        function serializeNode(n: ts.Node): any {
-            var o: any = { kind: getKindName(n.kind) };
-            o.containsParseError = ts.containsParseError(n);
-
-            ts.forEach(Object.getOwnPropertyNames(n), propertyName => {
-                switch (propertyName) {
-                    case "parent":
-                    case "symbol":
-                    case "locals":
-                    case "localSymbol":
-                    case "kind":
-                    case "semanticDiagnostics":
-                    case "id":
-                    case "nodeCount":
-                    case "symbolCount":
-                    case "identifierCount":
-                        // Blacklist of items we never put in the baseline file.
-                        break;
-
-                    case "flags":
-                        // Print out flags with their enum names.
-                        o[propertyName] = getNodeFlagName(n.flags);
-                        break;
-
-                    case "parserContextFlags":
-                        o[propertyName] = getParserContextFlagName(n.parserContextFlags);
-                        break;
-
-                    case "referenceDiagnostics":
-                    case "parseDiagnostics":
-                    case "grammarDiagnostics":
-                        o[propertyName] = Utils.convertDiagnostics((<any>n)[propertyName]);
-                        break;
-
-                    case "nextContainer":
-                        if (n.nextContainer) {
-                            o[propertyName] = { kind: n.nextContainer.kind, pos: n.nextContainer.pos, end: n.nextContainer.end };
-                        }
-                        break;
-
-                    case "text":
-                        // Include 'text' field for identifiers/literals, but not for source files.
-                        if (n.kind !== ts.SyntaxKind.SourceFile) {
-                            o[propertyName] = (<any>n)[propertyName];
-                        }
-                        break;
-
-                    default:
-                        o[propertyName] = (<any>n)[propertyName];
-                }
-
-                return undefined;
-            });
-
-            return o;
-        }
-
-        return JSON.stringify(file, (k, v) => {
-            return Test262BaselineRunner.isNodeOrArray(v) ? serializeNode(v) : v;
-        }, "    ");
-    }
-
-    private static isNodeOrArray(a: any): boolean {
-        return a !== undefined && typeof a.pos === "number";
-    }
-
     private runTest(filePath: string) {
         describe('test262 test for ' + filePath, () => {
             // Mocha holds onto the closure environment of the describe callback even after the test is done.
@@ -183,7 +85,7 @@ class Test262BaselineRunner extends RunnerBase {
             it('has the expected AST',() => {
                 Harness.Baseline.runBaseline('has the expected AST', testState.filename + '.AST.txt',() => {
                     var sourceFile = testState.checker.getProgram().getSourceFile(Test262BaselineRunner.getTestFilePath(testState.filename));
-                    return Test262BaselineRunner.serializeSourceFile(sourceFile);
+                    return Utils.sourceFileToJSON(sourceFile);
                 }, false, Test262BaselineRunner.baselineOptions);
             });
         });