diff --git a/src/index.ts b/src/index.ts
index c94f4a60..18e405d4 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -10,10 +10,8 @@ export interface RimrafOptions {
   maxBackoff?: number
 }
 
-/* c8 ignore start */
 const typeOrUndef = (val: any, t: string) =>
   typeof val === 'undefined' || typeof val === t
-/* c8 ignore stop */
 
 export const isRimrafOptions = (o: any): o is RimrafOptions =>
   !!o &&
@@ -25,7 +23,6 @@ export const isRimrafOptions = (o: any): o is RimrafOptions =>
   typeOrUndef(o.backoff, 'number') &&
   typeOrUndef(o.maxBackoff, 'number')
 
-/* c8 ignore start */
 export const assertRimrafOptions: (o: any) => void = (
   o: any
 ): asserts o is RimrafOptions => {
@@ -33,7 +30,6 @@ export const assertRimrafOptions: (o: any) => void = (
     throw new Error('invalid rimraf options')
   }
 }
-/* c8 ignore stop */
 
 import { rimrafManual, rimrafManualSync } from './rimraf-manual.js'
 import { rimrafMoveRemove, rimrafMoveRemoveSync } from './rimraf-move-remove.js'
diff --git a/test/opt-arg.js b/test/opt-arg.js
index cf14d13d..f1460ac7 100644
--- a/test/opt-arg.js
+++ b/test/opt-arg.js
@@ -3,3 +3,8 @@ const optArg = require('../dist/cjs/src/opt-arg.js').default
 const opt = { a: 1 }
 t.equal(optArg(opt), opt, 'returns object if provided')
 t.same(optArg(), {}, 'returns new object otherwise')
+
+t.throws(() => optArg(true))
+t.throws(() => optArg(null))
+t.throws(() => optArg('hello'))
+t.throws(() => optArg({ maxRetries: 'banana' }))