diff --git a/vendor/exTpl/Expression.php b/vendor/exTpl/Expression.php
index ced08b59a6875c562905f4b64216d427496b1e20..35ea4581001f316024ae8f380cd237b3b3c503c0 100644
--- a/vendor/exTpl/Expression.php
+++ b/vendor/exTpl/Expression.php
@@ -320,7 +320,7 @@ class FunctionExpression implements Expression
             $arguments[] = $expr->value($context);
         }
 
-        if (is_callable($callable)) {
+        if ($callable instanceof \Closure) {
             return call_user_func_array($callable, $arguments);
         }
 
diff --git a/vendor/exTpl/Template.php b/vendor/exTpl/Template.php
index 0be46bf85fff6eda33c39e91d687ba16fec49ef2..9d5be04be159aa9614d743c2a586ba4963be3c7b 100644
--- a/vendor/exTpl/Template.php
+++ b/vendor/exTpl/Template.php
@@ -49,7 +49,10 @@ class Template
     public function __construct($string)
     {
         $this->template = new ArrayNode();
-        $this->functions = array('count' => 'count', 'strlen' => 'mb_strlen');
+        $this->functions = array(
+            'count' => function($a) { return count($a); },
+            'strlen' => function($a) { return mb_strlen($a); }
+        );
         self::parseTemplate($this->template, $string, 0);
     }
 
diff --git a/vendor/exTpl/template_test.php b/vendor/exTpl/template_test.php
index b794a820a1b032acb8b5a38ba2c43ef5754b60d9..62aee1c555bc18a4cdbee81784e2c76b53bda429 100644
--- a/vendor/exTpl/template_test.php
+++ b/vendor/exTpl/template_test.php
@@ -168,8 +168,12 @@ class template_test extends PHPUnit\Framework\TestCase
 
     public function testFilters()
     {
-        $bindings = array('pi' => 3.14159, 'format_number' => 'number_format', 'upper' => 'strtoupper');
-        $template = '{pi|format_number(3) ~ ":" ~ "foobar"|upper}';
+        $bindings = array(
+            'pi' => 3.14159,
+            'format' => function($a, $b) { return number_format($a, $b); },
+            'upper' => function($a) { return strtoupper($a); }
+        );
+        $template = '{pi|format(3) ~ ":" ~ "foobar"|upper}';
         $expected = '3.142:FOOBAR';
         $tmpl_obj = new Template($template);
 
@@ -178,7 +182,7 @@ class template_test extends PHPUnit\Framework\TestCase
 
     public function testRawFilter()
     {
-        $bindings = array('foo' => '<img>', 'upper' => 'strtoupper');
+        $bindings = array('foo' => '<img>', 'upper' => function($a) { return strtoupper($a); });
         $template = '{foo}:{foo|upper|raw}';
         $expected = '&lt;img&gt;:<IMG>';
         $tmpl_obj = new Template($template);