diff --git a/src/internal/form.ts b/src/internal/form.ts
index 46c5a44a..5cef2636 100644
--- a/src/internal/form.ts
+++ b/src/internal/form.ts
@@ -72,9 +72,8 @@ export class FormControlController implements ReactiveController {
         const formId = input.form;
 
         if (formId) {
-          const root = input.getRootNode() as Document | ShadowRoot;
-
-          const form = root.getElementById(formId);
+          const root = input.getRootNode() as Document | ShadowRoot | HTMLElement;
+          const form = root.querySelector(`#${formId}`);
 
           if (form) {
             return form as HTMLFormElement;