diff --git a/utils/tabbable.ts b/utils/tabbable.ts
index 37dafb131..93c49de4e 100644
--- a/utils/tabbable.ts
+++ b/utils/tabbable.ts
@@ -47,17 +47,21 @@ export function focusable(element: HTMLElement, isTabIndexNotNaN: boolean) {
 }
 
 export function tabbable(element: HTMLElement) {
-  let tabIndex = element.getAttribute("tabindex")
-  //@ts-ignore
-  if (tabIndex === null) tabIndex = undefined
-  //@ts-ignore
-  const isTabIndexNaN = isNaN(tabIndex)
-  //@ts-ignore
+  const tabIndexAttr = element.getAttribute("tabindex")
+  const tabIndex = tabIndexAttr !== null ? Number(tabIndexAttr) : undefined
+  const isTabIndexNaN = tabIndex === undefined || isNaN(tabIndex)
+
   return (isTabIndexNaN || tabIndex >= 0) && focusable(element, !isTabIndexNaN)
 }
 
 export default function findTabbableDescendants(
-  element: HTMLElement
+  element: HTMLElement | null | undefined
 ): HTMLElement[] {
-  return [].slice.call(element.querySelectorAll("*"), 0).filter(tabbable)
+  if (!(element instanceof HTMLElement)) {
+    return []
+  }
+
+  return Array.from(element.querySelectorAll("*"))
+    .filter((el): el is HTMLElement => el instanceof HTMLElement)
+    .filter(tabbable)
 }