diff --git a/program/lib/Roundcube/bootstrap.php b/program/lib/Roundcube/bootstrap.php
index d84bfc1cc..fca751df7 100644
--- a/program/lib/Roundcube/bootstrap.php
+++ b/program/lib/Roundcube/bootstrap.php
@@ -326,7 +326,7 @@ function array_first($array)
 function asciiwords($str, $css_id = false, $replace_with = '')
 {
     $allowed = 'a-z0-9\_\-' . (!$css_id ? '\.' : '');
-    return preg_replace("/[^$allowed]+/i", $replace_with, $str);
+    return preg_replace("/[^$allowed]+/i", $replace_with, (string) $str);
 }
 
 /**
@@ -340,7 +340,7 @@ function asciiwords($str, $css_id = false, $replace_with = '')
 function is_ascii($str, $control_chars = true)
 {
     $regexp = $control_chars ? '/[^\x00-\x7F]/' : '/[^\x20-\x7E]/';
-    return preg_match($regexp, $str) ? false : true;
+    return preg_match($regexp, (string) $str) ? false : true;
 }
 
 /**
diff --git a/program/lib/Roundcube/rcube.php b/program/lib/Roundcube/rcube.php
index 0b6915f67..f87033863 100644
--- a/program/lib/Roundcube/rcube.php
+++ b/program/lib/Roundcube/rcube.php
@@ -833,7 +833,7 @@ class rcube
             $lang = $rcube_language_aliases[$lang];
         }
         // try the first two chars
-        else if (!isset($rcube_languages[$lang])) {
+        else if ($lang && !isset($rcube_languages[$lang])) {
             $short = substr($lang, 0, 2);
 
             // check if we have an alias for the short language code
@@ -846,7 +846,7 @@ class rcube
             }
         }
 
-        if (!isset($rcube_languages[$lang]) || !is_dir(RCUBE_LOCALIZATION_DIR . $lang)) {
+        if (!$lang || !isset($rcube_languages[$lang]) || !is_dir(RCUBE_LOCALIZATION_DIR . $lang)) {
             $lang = 'en_US';
         }