diff --git a/CHANGELOG b/CHANGELOG
index a73beb7de8..66c073fc32 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,6 @@
 * 2.12.5 (2020-XX-XX)
 
- * n/a
+ * Add a check to ensure that iconv() is defined
 
 * 2.12.4 (2020-02-11)
 
diff --git a/src/Extension/CoreExtension.php b/src/Extension/CoreExtension.php
index 360efb8499..8bc9c0d632 100644
--- a/src/Extension/CoreExtension.php
+++ b/src/Extension/CoreExtension.php
@@ -411,7 +411,7 @@ function twig_random(Environment $env, $values = null, $max = null)
         $charset = $env->getCharset();
 
         if ('UTF-8' !== $charset) {
-            $values = iconv($charset, 'UTF-8', $values);
+            $values = twig_convert_encoding($values, 'UTF-8', $charset);
         }
 
         // unicode version of str_split()
@@ -420,7 +420,7 @@ function twig_random(Environment $env, $values = null, $max = null)
 
         if ('UTF-8' !== $charset) {
             foreach ($values as $i => $value) {
-                $values[$i] = iconv('UTF-8', $charset, $value);
+                $values[$i] = twig_convert_encoding($value, $charset, 'UTF-8');
             }
         }
     }
@@ -885,7 +885,7 @@ function twig_reverse_filter(Environment $env, $item, $preserveKeys = false)
     $charset = $env->getCharset();
 
     if ('UTF-8' !== $charset) {
-        $item = iconv($charset, 'UTF-8', $string);
+        $item = twig_convert_encoding($string, 'UTF-8', $charset);
     }
 
     preg_match_all('/./us', $item, $matches);
@@ -893,7 +893,7 @@ function twig_reverse_filter(Environment $env, $item, $preserveKeys = false)
     $string = implode('', array_reverse($matches[0]));
 
     if ('UTF-8' !== $charset) {
-        $string = iconv('UTF-8', $charset, $string);
+        $string = twig_convert_encoding($string, $charset, 'UTF-8');
     }
 
     return $string;
@@ -997,6 +997,10 @@ function twig_spaceless($content)
 
 function twig_convert_encoding($string, $to, $from)
 {
+    if (!function_exists('iconv')) {
+        throw new RuntimeError('Unable to convert encoding: required function iconv() does not exist. You should install ext-iconv or symfony/polyfill-iconv.');
+    }
+
     return iconv($from, $to, $string);
 }
 
diff --git a/src/Extension/EscaperExtension.php b/src/Extension/EscaperExtension.php
index b8dabccf11..136f75f702 100644
--- a/src/Extension/EscaperExtension.php
+++ b/src/Extension/EscaperExtension.php
@@ -244,7 +244,7 @@ function twig_escape_filter(Environment $env, $string, $strategy = 'html', $char
                 return htmlspecialchars($string, ENT_QUOTES | ENT_SUBSTITUTE, $charset);
             }
 
-            $string = iconv($charset, 'UTF-8', $string);
+            $string = twig_convert_encoding($string, 'UTF-8', $charset);
             $string = htmlspecialchars($string, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
 
             return iconv('UTF-8', $charset, $string);
@@ -253,7 +253,7 @@ function twig_escape_filter(Environment $env, $string, $strategy = 'html', $char
             // escape all non-alphanumeric characters
             // into their \x or \uHHHH representations
             if ('UTF-8' !== $charset) {
-                $string = iconv($charset, 'UTF-8', $string);
+                $string = twig_convert_encoding($string, 'UTF-8', $charset);
             }
 
             if (!preg_match('//u', $string)) {
@@ -301,7 +301,7 @@ function twig_escape_filter(Environment $env, $string, $strategy = 'html', $char
 
         case 'css':
             if ('UTF-8' !== $charset) {
-                $string = iconv($charset, 'UTF-8', $string);
+                $string = twig_convert_encoding($string, 'UTF-8', $charset);
             }
 
             if (!preg_match('//u', $string)) {
@@ -322,7 +322,7 @@ function twig_escape_filter(Environment $env, $string, $strategy = 'html', $char
 
         case 'html_attr':
             if ('UTF-8' !== $charset) {
-                $string = iconv($charset, 'UTF-8', $string);
+                $string = twig_convert_encoding($string, 'UTF-8', $charset);
             }
 
             if (!preg_match('//u', $string)) {