diff --git a/app/src/main/kotlin/com/simplemobiletools/filemanager/helpers/Constants.kt b/app/src/main/kotlin/com/simplemobiletools/filemanager/helpers/Constants.kt
index 2a4ed56d..46058b8c 100644
--- a/app/src/main/kotlin/com/simplemobiletools/filemanager/helpers/Constants.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/filemanager/helpers/Constants.kt
@@ -1,14 +1,13 @@
 package com.simplemobiletools.filemanager.helpers
 
-val PATH = "path"
+const val PATH = "path"
 
 // shared preferences
-val SHOW_HIDDEN = "show_hidden"
-val HOME_FOLDER = "home_folder"
-val FAVORITES = "favorites"
-val SORT_ORDER = "sort_order"
-val SORT_FOLDER_PREFIX = "sort_folder_"
-val TEMPORARILY_SHOW_HIDDEN = "temporarily_show_hidden"
-val IS_ROOT_AVAILABLE = "is_root_available"
-val ENABLE_ROOT_ACCESS = "enable_root_access"
-val LS_HAS_HARD_LINKS_COLUMN = "ls_has_hard_links_column"
+const val SHOW_HIDDEN = "show_hidden"
+const val HOME_FOLDER = "home_folder"
+const val FAVORITES = "favorites"
+const val SORT_ORDER = "sort_order"
+const val SORT_FOLDER_PREFIX = "sort_folder_"
+const val TEMPORARILY_SHOW_HIDDEN = "temporarily_show_hidden"
+const val IS_ROOT_AVAILABLE = "is_root_available"
+const val ENABLE_ROOT_ACCESS = "enable_root_access"
diff --git a/build.gradle b/build.gradle
index 89e92a15..66c86d61 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,7 +1,7 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
 buildscript {
-    ext.kotlin_version = '1.2.0'
+    ext.kotlin_version = '1.2.21'
 
     repositories {
         jcenter()