diff --git a/lib/Ftree/Prefs/Expanded.php b/lib/Ftree/Prefs/Expanded.php
index 5b35a8de7..8ecd147bc 100644
--- a/lib/Ftree/Prefs/Expanded.php
+++ b/lib/Ftree/Prefs/Expanded.php
@@ -41,8 +41,13 @@ public function __construct()
     {
         global $prefs;
 
-        if (($folders = @unserialize($prefs->getValue('expanded_folders'), array('allowed_classes' => false))) &&
-            is_array($folders)) {
+        $value = $prefs->getValue('expanded_folders');
+        $folders = $value ? json_decode($value, true) : array();
+        if (null === $folders && json_last_error() === JSON_ERROR_SYNTAX) {
+            // TODO: Remove backward compatibility with stored values
+            $folders = @unserialize($value, array('allowed_classes' => false));
+        }
+        if (is_array($folders)) {
             $this->_data = $folders;
         }
 
@@ -54,7 +59,7 @@ public function __construct()
      */
     public function shutdown()
     {
-        $GLOBALS['prefs']->setValue('expanded_folders', serialize($this->_data));
+        $GLOBALS['prefs']->setValue('expanded_folders', json_encode($this->_data, JSON_FORCE_OBJECT));
     }
 
     /**
diff --git a/lib/Ftree/Prefs/Poll.php b/lib/Ftree/Prefs/Poll.php
index bf961091d..717b616f7 100644
--- a/lib/Ftree/Prefs/Poll.php
+++ b/lib/Ftree/Prefs/Poll.php
@@ -47,7 +47,13 @@ public function __construct(IMP_Ftree $ftree)
             $this->_data = array('INBOX' => 1);
 
             /* Add the list of polled mailboxes from the prefs. */
-            if ($nav_poll = @unserialize($prefs->getValue('nav_poll'), array('allowed_classes' => false))) {
+            $value = $prefs->getValue('nav_poll');
+            $nav_poll = $value ? json_decode($value, true) : array();
+            if (null === $nav_poll && json_last_error() === JSON_ERROR_SYNTAX) {
+                // TODO: Remove backward compatibility with stored values
+                $nav_poll = @unserialize($value, array('allowed_classes' => false));
+            }
+            if ($nav_poll) {
                 $this->_data += $nav_poll;
             }
 
@@ -59,7 +65,7 @@ public function __construct(IMP_Ftree $ftree)
      */
     public function shutdown()
     {
-        $GLOBALS['prefs']->setValue('nav_poll', serialize($this->_data));
+        $GLOBALS['prefs']->setValue('nav_poll', json_encode($this->_data, JSON_FORCE_OBJECT));
     }
 
     /**
diff --git a/lib/Prefs/Sort.php b/lib/Prefs/Sort.php
index f9c834caf..0710b0b67 100644
--- a/lib/Prefs/Sort.php
+++ b/lib/Prefs/Sort.php
@@ -39,7 +39,12 @@ public function __construct()
     {
         global $prefs;
 
-        $sortpref = @unserialize($prefs->getValue(self::SORTPREF), array('allowed_classes' => false));
+        $value = $prefs->getValue(self::SORTPREF);
+        $sortpref = $value ? json_decode($value, true) : array();
+        if (null === $sortpref && json_last_error() === JSON_ERROR_SYNTAX) {
+            // TODO: Remove backward compatibility with stored values
+            $sortpref = @unserialize($value, array('allowed_classes' => false));
+        }
         if (is_array($sortpref)) {
             $this->_sortpref = $sortpref;
         }
@@ -106,7 +111,7 @@ public function newSortbyValue($sortby)
      */
     protected function _save()
     {
-        $GLOBALS['prefs']->setValue(self::SORTPREF, serialize($this->_sortpref));
+        $GLOBALS['prefs']->setValue(self::SORTPREF, json_encode($this->_sortpref, JSON_FORCE_OBJECT));
     }
 
     /* ArrayAccess methods. */