diff --git a/icingaweb2.ruleset.xml b/icingaweb2.ruleset.xml
index 93cb742cc..537a6be9b 100644
--- a/icingaweb2.ruleset.xml
+++ b/icingaweb2.ruleset.xml
@@ -22,6 +22,7 @@
         <exclude-pattern>library/Icinga/Application/LegacyWeb.php</exclude-pattern>
         <exclude-pattern>library/Icinga/Application/Web.php</exclude-pattern>
         <exclude-pattern>library/Icinga/File/Pdf.php</exclude-pattern>
+        <exclude-pattern>library/Icinga/Util/LessParser.php</exclude-pattern>
         <exclude-pattern>modules/doc/library/Doc/Renderer/DocSectionRenderer.php</exclude-pattern>
         <exclude-pattern>modules/monitoring/library/Monitoring/Plugin.php</exclude-pattern>
     </rule>
diff --git a/library/Icinga/Util/LessParser.php b/library/Icinga/Util/LessParser.php
new file mode 100644
index 000000000..84541fd8e
--- /dev/null
+++ b/library/Icinga/Util/LessParser.php
@@ -0,0 +1,38 @@
+<?php
+/* Icinga Web 2 | (c) 2021 Icinga GmbH | GPLv2+ */
+
+namespace Icinga\Util;
+
+use Exception;
+use lessc;
+use Icinga\Application\Logger;
+
+require_once 'lessphp/lessc.inc.php';
+
+class LessParser extends lessc
+{
+    protected function get($name)
+    {
+        try {
+            return parent::get($name);
+        } catch (Exception $e) {
+            Logger::error($e->getMessage());
+        }
+
+        return ['string', '', []];
+    }
+
+    protected function compileProp($prop, $block, $out)
+    {
+        try {
+            parent::compileProp($prop, $block, $out);
+        } catch (Exception $e) {
+            if (strpos($e->getMessage(), 'is undefined:') === false) {
+                // We silence mixin errors only
+                throw $e;
+            }
+
+            Logger::error($e->getMessage());
+        }
+    }
+}
diff --git a/library/Icinga/Web/LessCompiler.php b/library/Icinga/Web/LessCompiler.php
index 1d9aec05c..55c0614da 100644
--- a/library/Icinga/Web/LessCompiler.php
+++ b/library/Icinga/Web/LessCompiler.php
@@ -4,7 +4,7 @@
 namespace Icinga\Web;
 
 use Icinga\Application\Logger;
-use lessc;
+use Icinga\Util\LessParser;
 
 /**
  * Compile LESS into CSS
@@ -16,7 +16,7 @@ class LessCompiler
     /**
      * lessphp compiler
      *
-     * @var lessc
+     * @var LessParser
      */
     protected $lessc;
 
@@ -60,8 +60,7 @@ class LessCompiler
      */
     public function __construct()
     {
-        require_once 'lessphp/lessc.inc.php';
-        $this->lessc = new lessc();
+        $this->lessc = new LessParser();
         // Discourage usage of import because we're caching based on an explicit list of LESS files to compile
         $this->lessc->importDisabled = true;
     }