diff --git a/bin/apply-compat-patches b/bin/apply-compat-patches
new file mode 100644
index 000000000..4eae52481
--- /dev/null
+++ b/bin/apply-compat-patches
@@ -0,0 +1,79 @@
+#!/usr/bin/env php
+<?php
+
+chdir(__DIR__ . '/..');
+
+$parserFiles = [
+    'platforms/joomla/lib_gantry5/compat/vendor/twig/twig/src/Parser.php',
+    'platforms/wordpress/gantry5/compat/vendor/twig/twig/src/Parser.php',
+];
+
+foreach ($parserFiles as $file) {
+    patch_twig_parser($file);
+}
+
+function patch_twig_parser($file)
+{
+    if (!is_file($file)) {
+        return;
+    }
+
+    $contents = file_get_contents($file);
+    if ($contents === false) {
+        throw new RuntimeException("Unable to read {$file}");
+    }
+
+    $contents = str_replace(
+        <<<'PHP'
+        if (null === $this->handlers) {
+            $this->handlers = $this->env->getTokenParsers();
+            $this->handlers->setParser($this);
+        }
+PHP,
+        <<<'PHP'
+        if (null === $this->handlers) {
+            $this->handlers = $this->env->getTokenParsers();
+            if (is_object($this->handlers) && method_exists($this->handlers, 'setParser')) {
+                $this->handlers->setParser($this);
+            } elseif (is_array($this->handlers)) {
+                foreach ($this->handlers as $handler) {
+                    if (is_object($handler) && method_exists($handler, 'setParser')) {
+                        $handler->setParser($this);
+                    }
+                }
+            }
+        }
+PHP,
+        $contents,
+        $count
+    );
+
+    if ($count === 0 && strpos($contents, 'foreach ($this->handlers as $handler)') === false) {
+        throw new RuntimeException("Unable to patch token parser setup in {$file}");
+    }
+
+    $contents = str_replace(
+        <<<'PHP'
+                    $subparser = $this->handlers->getTokenParser($token->getValue());
+PHP,
+        <<<'PHP'
+                    if (is_object($this->handlers) && method_exists($this->handlers, 'getTokenParser')) {
+                        $subparser = $this->handlers->getTokenParser($token->getValue());
+                    } elseif (is_array($this->handlers)) {
+                        $subparser = isset($this->handlers[$token->getValue()]) ? $this->handlers[$token->getValue()] : null;
+                    } else {
+                        $subparser = null;
+                    }
+PHP,
+        $contents,
+        $count
+    );
+
+    if ($count === 0 && strpos($contents, 'isset($this->handlers[$token->getValue()])') === false) {
+        throw new RuntimeException("Unable to patch token parser lookup in {$file}");
+    }
+
+    if (file_put_contents($file, $contents) === false) {
+        throw new RuntimeException("Unable to write {$file}");
+    }
+}
diff --git a/bin/composer-install b/bin/composer-install
index a34b669a4..8aefeadca 100755
--- a/bin/composer-install
+++ b/bin/composer-install
@@ -24,6 +24,9 @@ composer_install('wordpress/gantry5', true);
 composer_install('wordpress/gantry5_debugbar', false);
 composer_install('wordpress/gantry5/compat', false);
 
+echo "# Applying compat vendor patches\n";
+require __DIR__ . '/apply-compat-patches';
+
 function composer_install($folder, $link)
 {
     chdir($folder);
diff --git a/bin/composer-update b/bin/composer-update
index 62dc0f482..7d17d095e 100755
--- a/bin/composer-update
+++ b/bin/composer-update
@@ -24,6 +24,9 @@ composer_update('wordpress/gantry5', true);
 composer_update('wordpress/gantry5_debugbar', false);
 composer_update('wordpress/gantry5/compat', false);
 
+echo "# Applying compat vendor patches\n";
+require __DIR__ . '/apply-compat-patches';
+
 function composer_update($folder, $link)
 {
     chdir($folder);
diff --git a/src/classes/Gantry/Component/Theme/AbstractTheme.php b/src/classes/Gantry/Component/Theme/AbstractTheme.php
index 961f4f08e..0f162555f 100644
--- a/src/classes/Gantry/Component/Theme/AbstractTheme.php
+++ b/src/classes/Gantry/Component/Theme/AbstractTheme.php
@@ -94,6 +94,8 @@ abstract class AbstractTheme
     public function extendTwig(Environment $twig, ?LoaderInterface $loader = null)
     {
         if ($twig->hasExtension(TwigExtension::class)) {
+            $this->addGantryTwigGlobal($twig);
+
             return $twig;
         }
 
@@ -104,6 +106,7 @@ abstract class AbstractTheme
         $this->setTwigLoaderPaths($loader);
 
         $twig->addExtension(new TwigExtension);
+        $this->addGantryTwigGlobal($twig);
 
         if (method_exists($this, 'toGrid')) {
             $filter = new TwigFilter('toGrid', [$this, 'toGrid']);
@@ -250,6 +253,18 @@ abstract class AbstractTheme
         return $loader;
     }
 
+    /**
+     * Ensure phpBB-provided Twig environments have Gantry available as a global.
+     *
+     * @param Environment $twig
+     */
+    protected function addGantryTwigGlobal(Environment $twig)
+    {
+        if (!array_key_exists('gantry', $twig->getGlobals())) {
+            $twig->addGlobal('gantry', static::gantry());
+        }
+    }
+
     /**
      * Get path to Twig cache.
      *