diff --git a/packages/conform-dom/submission.ts b/packages/conform-dom/submission.ts
index c1e2b594..eef241a3 100644
--- a/packages/conform-dom/submission.ts
+++ b/packages/conform-dom/submission.ts
@@ -524,14 +524,11 @@ export function setListState(
 	});
 }
 
-export function serialize<Schema>(
-	defaultValue: DefaultValue<Schema>,
-): FormValue<Schema> {
+export function serialize<Schema>(defaultValue: Schema): FormValue<Schema> {
 	if (isPlainObject(defaultValue)) {
 		// @ts-expect-error FIXME
 		return Object.entries(defaultValue).reduce<Record<string, unknown>>(
 			(result, [key, value]) => {
-				// @ts-ignore-error FIXME
 				result[key] = serialize(value);
 				return result;
 			},
@@ -540,16 +537,16 @@ export function serialize<Schema>(
 	} else if (Array.isArray(defaultValue)) {
 		// @ts-expect-error FIXME
 		return defaultValue.map(serialize);
-	} else if (
-		// @ts-ignore-error FIXME
-		defaultValue instanceof Date
-	) {
+	} else if (defaultValue instanceof Date) {
 		// @ts-expect-error FIXME
 		return defaultValue.toISOString();
 	} else if (typeof defaultValue === 'boolean') {
 		// @ts-expect-error FIXME
 		return defaultValue ? 'on' : undefined;
-	} else if (typeof defaultValue === 'number') {
+	} else if (
+		typeof defaultValue === 'number' ||
+		typeof defaultValue === 'bigint'
+	) {
 		// @ts-expect-error FIXME
 		return defaultValue.toString();
 	} else {