diff --git a/src/compiler/moduleNameResolver.ts b/src/compiler/moduleNameResolver.ts
index c35bf3da28c..f9fbe5b01c1 100644
--- a/src/compiler/moduleNameResolver.ts
+++ b/src/compiler/moduleNameResolver.ts
@@ -135,7 +135,7 @@ namespace ts {
         }
 
         let typeRoots: string[];
-        forEachAncestorDirectory(currentDirectory, directory => {
+        forEachAncestorDirectory(ts.normalizePath(currentDirectory), directory => {
             const atTypes = combinePaths(directory, nodeModulesAtTypes);
             if (host.directoryExists(atTypes)) {
                 (typeRoots || (typeRoots = [])).push(atTypes);
@@ -1060,4 +1060,4 @@ namespace ts {
             directory = parentPath;
         }
     }
-}
\ No newline at end of file
+}