diff --git a/lib/helpers/resolveConfig.js b/lib/helpers/resolveConfig.js
index f5ff1898..4d931c64 100644
--- a/lib/helpers/resolveConfig.js
+++ b/lib/helpers/resolveConfig.js
@@ -7,6 +7,19 @@ import mergeConfig from '../core/mergeConfig.js';
 import AxiosHeaders from '../core/AxiosHeaders.js';
 import buildURL from './buildURL.js';
 
+/**
+ * Encode a UTF-8 string to a Latin-1 byte string for use with btoa().
+ * This is a modern replacement for the deprecated unescape(encodeURIComponent(str)) pattern.
+ *
+ * @param {string} str The string to encode
+ *
+ * @returns {string} UTF-8 bytes as a Latin-1 string
+ */
+const encodeUTF8 = (str) => encodeURIComponent(str).replace(
+  /%([0-9A-F]{2})/gi,
+  (_, hex) => String.fromCharCode(parseInt(hex, 16))
+);
+
 export default (config) => {
   const newConfig = mergeConfig({}, config);
 
@@ -34,14 +47,8 @@ export default (config) => {
 
   // HTTP basic authentication
   if (auth) {
-    headers.set(
-      'Authorization',
-      'Basic ' +
-        btoa(
-          (auth.username || '') +
-            ':' +
-            (auth.password ? unescape(encodeURIComponent(auth.password)) : '')
-        )
+    headers.set('Authorization', 'Basic ' +
+      btoa((auth.username || '') + ':' + (auth.password ? encodeUTF8(auth.password) : ''))
     );
   }
 
diff --git a/lib/utils.js b/lib/utils.js
index 77f395e9..ae2a440b 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -225,7 +225,7 @@ const isBlob = kindOfTest('Blob');
  *
  * @param {*} val The value to test
  *
- * @returns {boolean} True if value is a File, otherwise false
+ * @returns {boolean} True if value is a FileList, otherwise false
  */
 const isFileList = kindOfTest('FileList');