diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index d9d23a92186..33c2da50c1a 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -623,7 +623,7 @@ namespace ts {
                 const hash = sys.createHash(data);
                 const mtimeBefore = sys.getModifiedTime(fileName);
 
-                if (mtimeBefore && outputFingerprints.hasOwnProperty(fileName)) {
+                if (mtimeBefore && hasProperty(outputFingerprints, fileName)) {
                     const fingerprint = outputFingerprints[fileName];
 
                     // If output has not been changed, and the file has no external modification
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 3f33df61a0f..9f7903d4201 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -229,6 +229,7 @@ namespace ts {
             const _path = require("path");
             const _os = require("os");
             const _crypto = require("crypto");
+            let hash: any;
 
             // average async stat takes about 30 microseconds
             // set chunk size to do 30 files in < 1 millisecond
@@ -560,10 +561,18 @@ namespace ts {
                 },
                 readDirectory,
                 getModifiedTime(path) {
-                    return _fs.existsSync(path) && _fs.statSync(path).mtime;
+                    try {
+                        return _fs.statSync(path).mtime;
+                    }
+                    catch (e) {
+                        return undefined;
+                    }
                 },
                 createHash(data) {
-                    const hash = _crypto.createHash("md5");
+                    if (!hash) {
+                        hash = _crypto.createHash("md5");
+                    }
+
                     hash.update(data);
                     return hash.digest("hex");
                 },