diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 7338448a3e7..561aeefcc6a 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -464,6 +464,12 @@ module ts {
         return pathLen > extLen && path.substr(pathLen - extLen, extLen) === extension;
     }
 
+    export function getCanonicalFileName(fileName: string): string {
+        // if underlying system can distinguish between two files whose names differs only in cases then file name already in canonical form.
+        // otherwise use toLowerCase as a canonical form.
+        return sys.useCaseSensitiveFileNames ? fileName : fileName.toLowerCase();
+    }
+
     export interface ObjectAllocator {
         getNodeConstructor(kind: SyntaxKind): new () => Node;
         getSymbolConstructor(): new (flags: SymbolFlags, name: string) => Symbol;
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 40e98821b68..7fdcac1795f 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -222,10 +222,4 @@ var sys: System = (function () {
     else {
         return undefined; // Unsupported host
     }
-})();
-
-function getCanonicalFileName(fileName: string): string {
-    // if underlying system can distinguish between two files whose names differs only in cases then file name already in canonical form.
-    // otherwise use toLowerCase as a canonical form.
-    return sys.useCaseSensitiveFileNames ? fileName : fileName.toLowerCase();
-}
+})();
\ No newline at end of file