diff --git a/Classes/ViewHelpers/ApplyRenderFunctionViewHelper.php b/Classes/ViewHelpers/ApplyRenderFunctionViewHelper.php
index cf97859..02539a1 100644
--- a/Classes/ViewHelpers/ApplyRenderFunctionViewHelper.php
+++ b/Classes/ViewHelpers/ApplyRenderFunctionViewHelper.php
@@ -7,15 +7,18 @@ namespace DigiComp\FluidRenderFunctions\ViewHelpers;
 use DigiComp\FluidRenderFunctions\InvokeRenderFunctionInterface;
 use DigiComp\FluidRenderFunctions\Utils\GeneratorClosureIterator;
 use DigiComp\FluidRenderFunctions\Utils\RenderableProxy;
+use DigiComp\FluidRenderFunctions\ViewHelpers\Traits\ValidateRenderFunctionTrait;
 use Neos\FluidAdaptor\Core\ViewHelper\AbstractViewHelper;
 
 class ApplyRenderFunctionViewHelper extends AbstractViewHelper
 {
+    use ValidateRenderFunctionTrait;
+
     public function initializeArguments(): void
     {
         parent::initializeArguments();
         $this->registerArgument('in', 'mixed', 'subject to apply the render function to');
-        $this->registerArgument('function', InvokeRenderFunctionInterface::class, 'render function to use', true);
+        $this->registerArgument('function', 'string', 'render function to use', true);
         $this->registerArgument(
             'force',
             'bool',
@@ -26,6 +29,12 @@ class ApplyRenderFunctionViewHelper extends AbstractViewHelper
         );
     }
 
+    public function validateArguments()
+    {
+        parent::validateArguments();
+        $this->validateRenderFunctionArgument('function');
+    }
+
     public function render()
     {
         $in = $this->arguments['in'];
diff --git a/Classes/ViewHelpers/RegisterRenderFunctionViewHelper.php b/Classes/ViewHelpers/RegisterRenderFunctionViewHelper.php
index 5db7772..511cae7 100644
--- a/Classes/ViewHelpers/RegisterRenderFunctionViewHelper.php
+++ b/Classes/ViewHelpers/RegisterRenderFunctionViewHelper.php
@@ -47,8 +47,9 @@ class RegisterRenderFunctionViewHelper extends AbstractViewHelper
         foreach ($this->childNodes as $childNode) {
             $transferNode->addChildNode($childNode);
         }
-        $this->renderingContext->getVariableProvider()
-            ->add($this->arguments['as'], new NodeRenderTransfer($transferNode, $this->arguments['subjectName']));
+        $renderer = new NodeRenderTransfer($transferNode, $this->arguments['subjectName']);
+        $this->renderingContext->getViewHelperVariableContainer()
+            ->add(static::class, $this->arguments['as'], $renderer);
         return '';
     }
 }
diff --git a/Classes/ViewHelpers/Traits/ValidateRenderFunctionTrait.php b/Classes/ViewHelpers/Traits/ValidateRenderFunctionTrait.php
new file mode 100644
index 0000000..c486f4d
--- /dev/null
+++ b/Classes/ViewHelpers/Traits/ValidateRenderFunctionTrait.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DigiComp\FluidRenderFunctions\ViewHelpers\Traits;
+
+use DigiComp\FluidRenderFunctions\InvokeRenderFunctionInterface;
+use DigiComp\FluidRenderFunctions\ViewHelpers\RegisterRenderFunctionViewHelper;
+
+trait ValidateRenderFunctionTrait
+{
+    public function validateRenderFunctionArgument(string $argumentName)
+    {
+        $renderFunction = $this->viewHelperVariableContainer->get(
+            RegisterRenderFunctionViewHelper::class,
+            $this->arguments[$argumentName]
+        );
+        if (!($renderFunction instanceof InvokeRenderFunctionInterface)) {
+            throw new \InvalidArgumentException(
+                'render function with name "' . $this->arguments[$argumentName] . '" has not been registered.',
+                1717293038
+            );
+        }
+        $this->arguments[$argumentName] = $renderFunction;
+    }
+}
diff --git a/README.md b/README.md
index 9dc2ced..f5f553a 100644
--- a/README.md
+++ b/README.md
@@ -13,5 +13,5 @@ FluidRenderFunctions to the rescue:
 <rf:registerRenderFunction as="renderBook" subjectName="myBook">
     {myBook.name} from {myBook.author.name}
 </rf:registerRenderFunction>
-<f:form.select options="{books -> rf:applyRenderFunction(function: renderBook)}" />
+<f:form.select options="{books -> rf:applyRenderFunction(function: 'renderBook')}" />
 ```
diff --git a/Resources/Private/Templates/Tests/Functional/Fixtures/Test/Index.html b/Resources/Private/Templates/Tests/Functional/Fixtures/Test/Index.html
index 369d8a4..ab764ae 100644
--- a/Resources/Private/Templates/Tests/Functional/Fixtures/Test/Index.html
+++ b/Resources/Private/Templates/Tests/Functional/Fixtures/Test/Index.html
@@ -4,5 +4,5 @@
     <rf:registerRenderFunction as="testFunc">
         {subject.name} is cool
     </rf:registerRenderFunction>
-    {test -> rf:applyRenderFunction(function: testFunc, force: true)}
+    {test -> rf:applyRenderFunction(function: 'testFunc', force: true)}
 </f:spaceless></f:section>
diff --git a/Resources/Private/Templates/Tests/Functional/Fixtures/Test/Select.html b/Resources/Private/Templates/Tests/Functional/Fixtures/Test/Select.html
index 1899cee..120ca49 100644
--- a/Resources/Private/Templates/Tests/Functional/Fixtures/Test/Select.html
+++ b/Resources/Private/Templates/Tests/Functional/Fixtures/Test/Select.html
@@ -4,5 +4,5 @@
     <rf:registerRenderFunction as="testFunc">
         {subject.name} is cool
     </rf:registerRenderFunction>
-    <f:form.select options="{testEntities -> rf:applyRenderFunction(function: testFunc)}" />
+    <f:form.select options="{testEntities -> rf:applyRenderFunction(function: 'testFunc')}" />
 </f:spaceless></f:section>