diff --git a/lib/helpers/toFormData.js b/lib/helpers/toFormData.js
index 327a979284..a41e966c03 100644
--- a/lib/helpers/toFormData.js
+++ b/lib/helpers/toFormData.js
@@ -152,7 +152,7 @@ function toFormData(obj, formData, options) {
         value = JSON.stringify(value);
       } else if (
         (utils.isArray(value) && isFlatArray(value)) ||
-        (utils.isFileList(value) || utils.endsWith(key, '[]') && (arr = utils.toArray(value))
+        ((utils.isFileList(value) || utils.endsWith(key, '[]')) && (arr = utils.toArray(value))
         )) {
         // eslint-disable-next-line no-param-reassign
         key = removeBrackets(key);