diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 671420468b..c09b70a0c6 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -152,7 +152,7 @@ module ts {
         let start = new Date().getTime();
 
         host = host || createCompilerHost(options);
-        let filesByName = createFileMap<SourceFile>(host.getCanonicalFileName);
+        let filesByName = createFileMap<SourceFile>(fileName => host.getCanonicalFileName(fileName));
 
         forEach(rootNames, name => processRootFile(name, /*isDefaultLib:*/ false));
         if (!skipDefaultLib) {