diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 9852b2354e2..d9d23a92186 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -559,6 +559,12 @@ namespace ts {
         sourceMap: false,
     };
 
+    interface OutputFingerprint {
+        hash: string;
+        byteOrderMark: boolean;
+        mtime: Date;
+    }
+
     export function createCompilerHost(options: CompilerOptions, setParentNodes?: boolean): CompilerHost {
         const existingDirectories: Map<boolean> = {};
 
@@ -609,11 +615,42 @@ namespace ts {
             }
         }
 
+        const outputFingerprints: Map<OutputFingerprint> =
+            options.watch && sys.createHash && sys.getModifiedTime ? {} : undefined;
+
+        const fileWriter: typeof sys.writeFile = outputFingerprints ?
+            (fileName, data, writeByteOrderMark) => {
+                const hash = sys.createHash(data);
+                const mtimeBefore = sys.getModifiedTime(fileName);
+
+                if (mtimeBefore && outputFingerprints.hasOwnProperty(fileName)) {
+                    const fingerprint = outputFingerprints[fileName];
+
+                    // If output has not been changed, and the file has no external modification
+                    if (fingerprint.byteOrderMark === writeByteOrderMark &&
+                        fingerprint.hash === hash &&
+                        fingerprint.mtime.getTime() === mtimeBefore.getTime()) {
+                        return;
+                    }
+                }
+
+                sys.writeFile(fileName, data, writeByteOrderMark);
+
+                const mtimeAfter = sys.getModifiedTime(fileName);
+
+                outputFingerprints[fileName] = {
+                    hash,
+                    byteOrderMark: writeByteOrderMark,
+                    mtime: mtimeAfter
+                };
+            } :
+            (fileName, data, writeByteOrderMark) => sys.writeFile(fileName, data, writeByteOrderMark);
+
         function writeFile(fileName: string, data: string, writeByteOrderMark: boolean, onError?: (message: string) => void) {
             try {
                 const start = new Date().getTime();
                 ensureDirectoriesExist(getDirectoryPath(normalizePath(fileName)));
-                sys.writeFile(fileName, data, writeByteOrderMark);
+                fileWriter(fileName, data, writeByteOrderMark);
                 ioWriteTime += new Date().getTime() - start;
             }
             catch (e) {
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 69277f65a92..3f33df61a0f 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -20,6 +20,8 @@ namespace ts {
         getExecutingFilePath(): string;
         getCurrentDirectory(): string;
         readDirectory(path: string, extension?: string, exclude?: string[]): string[];
+        getModifiedTime?(path: string): Date;
+        createHash?(data: string): string;
         getMemoryUsage?(): number;
         exit(exitCode?: number): void;
     }
@@ -39,15 +41,6 @@ namespace ts {
         referenceCount: number;
     }
 
-    interface OutputFingerprint {
-        hash: string;
-        mtime: Date;
-    }
-
-    interface OutputFingerprintMap {
-        [fileName: string]: OutputFingerprint;
-    }
-
     declare var require: any;
     declare var module: any;
     declare var process: any;
@@ -449,26 +442,12 @@ namespace ts {
                 return buffer.toString("utf8");
             }
 
-            const outputFingerprintMap: OutputFingerprintMap = {};
-
             function writeFile(fileName: string, data: string, writeByteOrderMark?: boolean): void {
                 // If a BOM is required, emit one
                 if (writeByteOrderMark) {
                     data = "\uFEFF" + data;
                 }
 
-                const md5 = getMd5(data);
-                const mtimeBefore = _fs.existsSync(fileName) && _fs.statSync(fileName).mtime;
-
-                if (mtimeBefore && outputFingerprintMap.hasOwnProperty(fileName)) {
-                    const fingerprint = outputFingerprintMap[fileName];
-
-                    // If output has not been changed, and the file has no external modification
-                    if (fingerprint.hash === md5 && fingerprint.mtime.getTime() === mtimeBefore.getTime()) {
-                        return;
-                    }
-                }
-
                 let fd: number;
 
                 try {
@@ -480,19 +459,6 @@ namespace ts {
                         _fs.closeSync(fd);
                     }
                 }
-
-                const mtimeAfter = _fs.statSync(fileName).mtime;
-
-                outputFingerprintMap[fileName] = {
-                    hash: md5,
-                    mtime: mtimeAfter
-                };
-            }
-
-            function getMd5(data: string): string {
-                const hash = _crypto.createHash("md5");
-                hash.update(data);
-                return hash.digest("hex");
             }
 
             function getCanonicalPath(path: string): string {
@@ -593,6 +559,14 @@ namespace ts {
                     return process.cwd();
                 },
                 readDirectory,
+                getModifiedTime(path) {
+                    return _fs.existsSync(path) && _fs.statSync(path).mtime;
+                },
+                createHash(data) {
+                    const hash = _crypto.createHash("md5");
+                    hash.update(data);
+                    return hash.digest("hex");
+                },
                 getMemoryUsage() {
                     if (global.gc) {
                         global.gc();