diff --git a/src/services/services.ts b/src/services/services.ts
index 4e7323e1b55..0069f53922d 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -1411,7 +1411,7 @@ module ts {
             return {
                 getSourceFile: (filename, languageVersion) => {
                     var sourceFile = getSourceFile(filename);
-                    return sourceFile ? sourceFile.getSourceFile() : null;
+                    return sourceFile && sourceFile.getSourceFile();
                 },
                 getCancellationToken: () => cancellationToken,
                 getCanonicalFileName: (filename) => useCaseSensitivefilenames ? filename : filename.toLowerCase(),