diff --git a/i18next/i18next.d.ts b/i18next/i18next.d.ts
index f39095459..3d24c9b96 100644
--- a/i18next/i18next.d.ts
+++ b/i18next/i18next.d.ts
@@ -23,7 +23,7 @@ interface I18nextOptions {
     preload?: string[];                     // Default value: []
     lowerCaseLng?: boolean;                    // Default value: false
     returnObjectTrees?: boolean;               // Default value: false
-    fallbackLng?: string;                   // Default value: 'dev'
+    fallbackLng?: string|boolean;           // Default value: 'dev'
     detectLngQS?: string;                   // Default value: 'setLng'
     ns?: any;                               // Default value: 'translation' (string), can also be an object
     nsseparator?: string;                   // Default value: '::'
@@ -135,4 +135,4 @@ declare module 'i18next' {
 
 declare module 'i18next-client' {
     export = i18n;
-}
\ No newline at end of file
+}