diff --git a/stlc-bidir/index.ts b/stlc-bidir/index.ts
index 6bade39..10428b7 100644
--- a/stlc-bidir/index.ts
+++ b/stlc-bidir/index.ts
@@ -227,7 +227,7 @@ const buildExpr = (s: string, c: TreeCursor): term => {
 export const parseExpr = (s: string) => {
   const tree = buildParser(parserSource("Expr"), {
     typeScript: true,
-    warn: false,
+    warn: () => {},
   }).parse(s);
 
   const cursor = tree.cursor();
@@ -238,7 +238,7 @@ export const parseExpr = (s: string) => {
 export const parseTy = (s: string) => {
   const tree = buildParser(parserSource("Ty"), {
     typeScript: true,
-    warn: false,
+    warn: () => {},
   }).parse(s);
 
   const cursor = tree.cursor();