diff --git a/backend/src/test/java/org/raddatz/familienarchiv/service/AnnotationServiceTest.java b/backend/src/test/java/org/raddatz/familienarchiv/service/AnnotationServiceTest.java
index 0534a7a3..bd3064a9 100644
--- a/backend/src/test/java/org/raddatz/familienarchiv/service/AnnotationServiceTest.java
+++ b/backend/src/test/java/org/raddatz/familienarchiv/service/AnnotationServiceTest.java
@@ -11,6 +11,7 @@ import org.raddatz.familienarchiv.exception.DomainException;
 import org.raddatz.familienarchiv.model.DocumentAnnotation;
 import org.raddatz.familienarchiv.repository.AnnotationRepository;
 import org.raddatz.familienarchiv.repository.TranscriptionBlockRepository;
+import org.springframework.dao.DataIntegrityViolationException;
 
 import java.util.List;
 import java.util.Optional;
@@ -22,6 +23,7 @@ import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
+import static org.springframework.http.HttpStatus.BAD_REQUEST;
 import static org.springframework.http.HttpStatus.FORBIDDEN;
 import static org.springframework.http.HttpStatus.NOT_FOUND;
 
@@ -241,6 +243,25 @@ class AnnotationServiceTest {
         verify(annotationRepository).save(annotation);
     }
 
+    @Test
+    void updateAnnotation_throwsAnnotationUpdateFailed_whenDbConstraintViolated() {
+        UUID docId = UUID.randomUUID();
+        UUID annotId = UUID.randomUUID();
+        DocumentAnnotation annotation = DocumentAnnotation.builder()
+                .id(annotId).documentId(docId)
+                .x(0.1).y(0.2).width(0.3).height(0.4).build();
+        when(annotationRepository.findByIdAndDocumentId(annotId, docId))
+                .thenReturn(Optional.of(annotation));
+        when(annotationRepository.save(any())).thenThrow(new DataIntegrityViolationException("constraint"));
+
+        UpdateAnnotationDTO dto = new UpdateAnnotationDTO();
+        dto.setX(1.5);
+
+        assertThatThrownBy(() -> annotationService.updateAnnotation(docId, annotId, dto))
+                .isInstanceOf(DomainException.class)
+                .satisfies(e -> assertThat(((DomainException) e).getStatus()).isEqualTo(BAD_REQUEST));
+    }
+
     // ─── listAnnotations ──────────────────────────────────────────────────────
 
     @Test