diff --git a/src/index.ts b/src/index.ts
index c8f62a743b89040c1d10a8ae3795bec8afcbc134..7cd7c1e98c1c9516b40f678627f51fd1adfa18c7 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -109,9 +109,9 @@ export function formatError(
       (name) => name !== "stack" && name !== "message"
     );
     if (propNames.length > 0) {
-      const props = {};
+      const props: Record<string, unknown> = {};
       propNames.forEach((name) => {
-        props[name] = err[name];
+        props[name] = (err as Record<string, object>)[name];
       });
 
       let propertiesString;