diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index ee6c9edc3b..e9f15b6fa8 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -508,6 +508,9 @@ namespace ts {
         echo(s: string): void;
         quit(exitCode?: number): void;
         fileExists(path: string): boolean;
+        deleteFile(path: string): boolean;
+        getModifiedTime(path: string): Date;
+        setModifiedTime(path: string, time: Date): void;
         directoryExists(path: string): boolean;
         createDirectory(path: string): void;
         resolvePath(path: string): string;
@@ -1135,6 +1138,9 @@ namespace ts {
                 },
                 resolvePath: ChakraHost.resolvePath,
                 fileExists: ChakraHost.fileExists,
+                deleteFile: ChakraHost.deleteFile,
+                getModifiedTime: ChakraHost.getModifiedTime,
+                setModifiedTime: ChakraHost.setModifiedTime,
                 directoryExists: ChakraHost.directoryExists,
                 createDirectory: ChakraHost.createDirectory,
                 getExecutingFilePath: () => ChakraHost.executingFile,
diff --git a/src/tsc/tsc.ts b/src/tsc/tsc.ts
index 47d2c0b5c7..97e239c8bc 100644
--- a/src/tsc/tsc.ts
+++ b/src/tsc/tsc.ts
@@ -19,9 +19,13 @@ namespace ts {
         }
     }
 
+    function defaultIsPretty() {
+        return !!sys.writeOutputIsTTY && sys.writeOutputIsTTY();
+    }
+
     function shouldBePretty(options: CompilerOptions) {
         if (typeof options.pretty === "undefined") {
-            return !!sys.writeOutputIsTTY && sys.writeOutputIsTTY();
+            return defaultIsPretty();
         }
         return options.pretty;
     }
@@ -50,7 +54,7 @@ namespace ts {
 
     export function executeCommandLine(args: string[]): void {
         if (args.length > 0 && ((args[0].toLowerCase() === "--build") || (args[0].toLowerCase() === "-b"))) {
-            const reportDiag = createDiagnosticReporter(sys, /*pretty*/ true);
+            const reportDiag = createDiagnosticReporter(sys, defaultIsPretty());
             const report = (message: DiagnosticMessage, ...args: string[]) => reportDiag(createCompilerDiagnostic(message, ...args));
             const buildHost: BuildHost = {
                 error: report,