diff --git a/app/Main.hs b/app/Main.hs
index 0c177f2bf..993c6c1d7 100644
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -36,6 +36,7 @@ main = do
   -- return ()
   document <- ts_document_make
   language <- ts_language_c
+  ts_document_set_language document language
   putStrLn $ "cSizeOf " ++ show (cSizeOf document)
 
 parseModuleFile :: FilePath -> IO (ParseResult HsModule)