diff --git a/backend/src/test/java/org/raddatz/familienarchiv/controller/TranscriptionBlockControllerTest.java b/backend/src/test/java/org/raddatz/familienarchiv/controller/TranscriptionBlockControllerTest.java
index 68ccacfb..0d39884a 100644
--- a/backend/src/test/java/org/raddatz/familienarchiv/controller/TranscriptionBlockControllerTest.java
+++ b/backend/src/test/java/org/raddatz/familienarchiv/controller/TranscriptionBlockControllerTest.java
@@ -251,6 +251,21 @@ class TranscriptionBlockControllerTest {
                 .andExpect(jsonPath("$.label").value("Anrede"));
     }
 
+    @Test
+    @WithMockUser(authorities = "WRITE_ALL")
+    void updateBlock_returns400_whenMentionedPersonDisplayNameExceeds200Chars() throws Exception {
+        when(userService.findByEmail(any())).thenReturn(mockUser());
+        String longName = "A".repeat(201);
+        String body = "{\"text\":\"x\",\"mentionedPersons\":[{\"personId\":\""
+                + UUID.randomUUID() + "\",\"displayName\":\"" + longName + "\"}]}";
+
+        mockMvc.perform(put(URL_BLOCK)
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content(body))
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.code").value("VALIDATION_ERROR"));
+    }
+
     @Test
     @WithMockUser(authorities = "WRITE_ALL")
     void updateBlock_returns404_whenBlockDoesNotExist() throws Exception {