diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index 534778fdab8f4..f27e7e1c1749a 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -1210,18 +1210,7 @@ namespace Harness {
         }
 
         export function minimalDiagnosticsToString(diagnostics: ts.Diagnostic[]) {
-            // This is basically copied from tsc.ts's reportError to replicate what tsc does
-            let errorOutput = "";
-            ts.forEach(diagnostics, diagnostic => {
-                if (diagnostic.file) {
-                    const lineAndCharacter = diagnostic.file.getLineAndCharacterOfPosition(diagnostic.start);
-                    errorOutput += diagnostic.file.fileName + "(" + (lineAndCharacter.line + 1) + "," + (lineAndCharacter.character + 1) + "): ";
-                }
-
-                errorOutput += ts.DiagnosticCategory[diagnostic.category].toLowerCase() + " TS" + diagnostic.code + ": " + ts.flattenDiagnosticMessageText(diagnostic.messageText, Harness.IO.newLine()) + Harness.IO.newLine();
-            });
-
-            return errorOutput;
+            return ts.formatDiagnostics(diagnostics, { getCanonicalFileName, getCurrentDirectory: () => "", getNewLine: () => Harness.IO.newLine() });
         }
 
         export function getErrorBaseline(inputFiles: TestFile[], diagnostics: ts.Diagnostic[]) {
diff --git a/src/harness/unittests/moduleResolution.ts b/src/harness/unittests/moduleResolution.ts
index b3f2102d903de..5f63889b08498 100644
--- a/src/harness/unittests/moduleResolution.ts
+++ b/src/harness/unittests/moduleResolution.ts
@@ -1,21 +1,6 @@
 /// <reference path="..\harness.ts" />
 
 namespace ts {
-    function diagnosticToString(diagnostic: Diagnostic) {
-        let output = "";
-
-        if (diagnostic.file) {
-            const loc = getLineAndCharacterOfPosition(diagnostic.file, diagnostic.start);
-
-            output += `${diagnostic.file.fileName}(${loc.line + 1},${loc.character + 1}): `;
-        }
-
-        const category = DiagnosticCategory[diagnostic.category].toLowerCase();
-        output += `${category} TS${diagnostic.code}: ${flattenDiagnosticMessageText(diagnostic.messageText, sys.newLine)}${sys.newLine}`;
-
-        return output;
-    }
-
     interface File {
         name: string;
         content?: string;
@@ -322,9 +307,9 @@ namespace ts {
 
             assert.equal(program.getSourceFiles().length, expectedFilesCount);
             const syntacticDiagnostics = program.getSyntacticDiagnostics();
-            assert.equal(syntacticDiagnostics.length, 0, `expect no syntactic diagnostics, got: ${JSON.stringify(syntacticDiagnostics.map(diagnosticToString))}`);
+            assert.equal(syntacticDiagnostics.length, 0, `expect no syntactic diagnostics, got: ${JSON.stringify(Harness.Compiler.minimalDiagnosticsToString(syntacticDiagnostics))}`);
             const semanticDiagnostics = program.getSemanticDiagnostics();
-            assert.equal(semanticDiagnostics.length, 0, `expect no semantic diagnostics, got: ${JSON.stringify(semanticDiagnostics.map(diagnosticToString))}`);
+            assert.equal(semanticDiagnostics.length, 0, `expect no semantic diagnostics, got: ${JSON.stringify(Harness.Compiler.minimalDiagnosticsToString(semanticDiagnostics))}`);
 
             // try to get file using a relative name
             for (const relativeFileName of relativeNamesToCheck) {
@@ -403,7 +388,7 @@ export = C;
             };
             const program = createProgram(rootFiles, options, host);
             const diagnostics = sortAndDeduplicateDiagnostics(program.getSemanticDiagnostics().concat(program.getOptionsDiagnostics()));
-            assert.equal(diagnostics.length, diagnosticCodes.length, `Incorrect number of expected diagnostics, expected ${diagnosticCodes.length}, got '${map(diagnostics, diagnosticToString).join("\r\n")}'`);
+            assert.equal(diagnostics.length, diagnosticCodes.length, `Incorrect number of expected diagnostics, expected ${diagnosticCodes.length}, got '${Harness.Compiler.minimalDiagnosticsToString(diagnostics)}'`);
             for (let i = 0; i < diagnosticCodes.length; i++) {
                 assert.equal(diagnostics[i].code, diagnosticCodes[i], `Expected diagnostic code ${diagnosticCodes[i]}, got '${diagnostics[i].code}': '${diagnostics[i].messageText}'`);
             }