diff --git a/Classes/DataProcessing/HighlightProcessor.php b/Classes/DataProcessing/HighlightProcessor.php
index b88292e..82733fb 100644
--- a/Classes/DataProcessing/HighlightProcessor.php
+++ b/Classes/DataProcessing/HighlightProcessor.php
@@ -46,13 +46,28 @@ public function process(ContentObjectRenderer $cObj, array $contentObjectConfigu
         $targetVariableName = $cObj->stdWrapValue('as', $processorConfiguration, 'bodytext_formatted');
         $highlight = GeneralUtility::makeInstance(Highlighter::class);
 
+        // The column is nullable, so a record can carry NULL rather than the empty
+        // string the TCA default writes. Normalise before deciding, because "??"
+        // only substitutes for NULL and would send it on to the highlighter.
+        $language = trim((string)($processedData['data']['code_language'] ?? ''));
+
+        $highlighted = null;
+        if ($language !== '') {
+            try {
+                $highlighted = $highlight->highlight($language, $processedData['data'][$fieldName]);
+            } catch (\DomainException $e) {
+                // The stored language is not registered - it may have been dropped from
+                // the list, or the record may come from an installation that had it.
+                // Detect instead, so a stale value does not take the page down.
+                $highlighted = null;
+            }
+        }
+
         // Let highlight.php decide which code language to use from all registered if "detect automatically" is selected.
-        if (!($processedData['data']['code_language'] ?? true)) {
+        if ($highlighted === null) {
             $languages = $highlight->listLanguages();
             $highlight->setAutodetectLanguages($languages);
             $highlighted = $highlight->highlightAuto($processedData['data'][$fieldName]);
-        } else {
-            $highlighted = $highlight->highlight($processedData['data']['code_language'], $processedData['data'][$fieldName]);
         }
 
         $processedData[$targetVariableName]['code'] = $highlighted->value;