diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index a5a3ec36fcc..2f5ff604df3 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -14,7 +14,7 @@ interface System {
     createDirectory(directoryName: string): void;
     getExecutingFilePath(): string;
     getCurrentDirectory(): string;
-    getMemoryUsage(): number;
+    getMemoryUsage?(): number;
     exit(exitCode?: number): void;
 }
 
@@ -128,9 +128,6 @@ var sys: System = (function () {
             getCurrentDirectory() {
                 return new ActiveXObject("WScript.Shell").CurrentDirectory;
             },
-            getMemoryUsage() {
-                return 0;
-            },
             exit(exitCode?: number): void {
                 try {
                     WScript.Quit(exitCode);
diff --git a/src/compiler/tsc.ts b/src/compiler/tsc.ts
index ca5624875eb..af425c337aa 100644
--- a/src/compiler/tsc.ts
+++ b/src/compiler/tsc.ts
@@ -337,14 +337,14 @@ module ts {
 
         reportDiagnostics(errors);
         if (commandLine.options.diagnostics) {
-            var memoryUsed = sys.getMemoryUsage();
+            var memoryUsed = sys.getMemoryUsage ? sys.getMemoryUsage() : -1;
             reportCountStatistic("Files", program.getSourceFiles().length);
             reportCountStatistic("Lines", countLines(program));
             reportCountStatistic("Nodes", checker ? checker.getNodeCount() : 0);
             reportCountStatistic("Identifiers", checker ? checker.getIdentifierCount() : 0);
             reportCountStatistic("Symbols", checker ? checker.getSymbolCount() : 0);
             reportCountStatistic("Types", checker ? checker.getTypeCount() : 0);
-            if (memoryUsed) {
+            if (memoryUsed >= 0) {
                 reportStatisticalValue("Memory used", Math.round(memoryUsed / 1000) + "K");
             }
             reportTimeStatistic("Parse time", bindStart - parseStart);