diff --git a/frontend/src/OnlineClassroom/ClassroomUserCreation.tsx b/frontend/src/OnlineClassroom/ClassroomUserCreation.tsx
index d32da0f..26e88a2 100644
--- a/frontend/src/OnlineClassroom/ClassroomUserCreation.tsx
+++ b/frontend/src/OnlineClassroom/ClassroomUserCreation.tsx
@@ -32,13 +32,18 @@ export function ClassroomUserCreation(props: {
         const maternalSurname = props.person.person_maternal_surname;
 
         // The username may be composed of A-Z & 0-9.
-        const user = `${firstName[0]}${secondName?.[0] ?? ""}${paternalSurname}${maternalSurname[0]}`
+        const user = `${firstName[0]}${secondName?.[0] ?? ""}${paternalSurname}${maternalSurname?.[0] ?? ""}`
             .toUpperCase()
             .replaceAll("Á", "A")
             .replaceAll("É", "E")
             .replaceAll("Í", "I")
             .replaceAll("Ó", "O")
             .replaceAll("Ú", "U")
+            .replaceAll("Ä", "A")
+            .replaceAll("Ë", "E")
+            .replaceAll("Ï", "I")
+            .replaceAll("Ö", "O")
+            .replaceAll("Ü", "U")
             .replaceAll("Ñ", "N")
             .replaceAll(" ", "")
             .replaceAll("-", "");