Don't error when trying to extend non-extensible errors

index.js

@@ -22,8 +22,13 @@ const decorateErrorWithCounts = (error, attemptNumber, options) => {
 	// Minus 1 from attemptNumber because the first attempt does not count as a retry
 	const retriesLeft = options.retries - (attemptNumber - 1);
 
-	error.attemptNumber = attemptNumber;
-	error.retriesLeft = retriesLeft;
+	try {
+		error.attemptNumber = attemptNumber;
+		error.retriesLeft = retriesLeft;
+	} catch {
+		// ignore errors trying to extend non-extensible errors
+	}
+
 	return error;
 };
 

test.js

@@ -328,3 +328,17 @@ test('should retry only when shouldRetry returns true', async t => {
 
 	t.is(index, 3);
 });
+
+test('can retry functions that throw non-extensible errors', async t => {
+	let index = 0;
+	const nonExtensibleError = Object.preventExtensions(new Error('non-extensible-error'));
+
+	const returnValue = await pRetry(async attemptNumber => {
+		await delay(40);
+		index++;
+		return attemptNumber === 3 ? fixture : Promise.reject(nonExtensibleError);
+	});
+
+	t.is(returnValue, fixture);
+	t.is(index, 3);
+});