diff --git a/frontend/src/certs/Registers/RegisterElement.tsx b/frontend/src/certs/Registers/RegisterElement.tsx
index eeb50d7..2fffd49 100644
--- a/frontend/src/certs/Registers/RegisterElement.tsx
+++ b/frontend/src/certs/Registers/RegisterElement.tsx
@@ -177,9 +177,17 @@ export function generateCert(person: Person, register: Register, coursesMap: {[c
     const personFullName = `${person.person_names} ${person.person_paternal_surname} ${person.person_maternal_surname}`;
 
     // Manage custom label
-    const certCustomLabel = register.register_custom_label === 1
-        ? ""
-        : customLabelsMap()[register.register_custom_label]?.custom_label_value ?? "";
+    let certCustomLabel = "";
+    if (register.register_custom_label === 1) {
+        certCustomLabel = "";
+    } else {
+        const customLabel = customLabelsMap()[register.register_custom_label];
+        if (customLabel === undefined) {
+            alert(`Error. No se encontró la denominación con id ${register.register_custom_label}`);
+            return;
+        }
+        certCustomLabel = customLabel.custom_label_value;
+    }
 
     const certCode = register.register_is_preview ? "0000" : register.register_code.toString().padStart(4, "0");