diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorController.java
index a2466aa9..a9109c13 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorController.java
@@ -84,7 +84,7 @@ public class HsOfficeDebitorController implements HsOfficeDebitorsApi {
         final var entityToSave = mapper.map(body, HsOfficeDebitorEntity.class);
         if ( body.getDebitorRel() != null ) {
             body.getDebitorRel().setType(DEBITOR.name());
-            final var debitorRel = mapper.map(body.getDebitorRel(), HsOfficeRelationRealEntity.class);
+            final var debitorRel = mapper.map("debitorRel.", body.getDebitorRel(), HsOfficeRelationRealEntity.class);
             validateEntityExists("debitorRel.anchorUuid", debitorRel.getAnchor());
             validateEntityExists("debitorRel.holderUuid", debitorRel.getHolder());
             validateEntityExists("debitorRel.contactUuid", debitorRel.getContact());
diff --git a/src/main/java/net/hostsharing/hsadminng/mapper/Mapper.java b/src/main/java/net/hostsharing/hsadminng/mapper/Mapper.java
index b568a0e6..aabfdfd9 100644
--- a/src/main/java/net/hostsharing/hsadminng/mapper/Mapper.java
+++ b/src/main/java/net/hostsharing/hsadminng/mapper/Mapper.java
@@ -47,6 +47,10 @@ abstract class Mapper extends ModelMapper {
 
     @Override
     public <D> D map(final Object source, final Class<D> destinationType) {
+        return map("", source, destinationType);
+    }
+
+    public <D> D map(final String namePrefix, final Object source, final Class<D> destinationType) {
         final var target = super.map(source, destinationType);
         for (Field f : getDeclaredFieldsIncludingSuperClasses(destinationType)) {
             if (f.getAnnotation(ManyToOne.class) == null) {
@@ -66,7 +70,7 @@ abstract class Mapper extends ModelMapper {
             if (subEntityUuid == null) {
                 continue;
             }
-            ReflectionUtils.setField(f, target, fetchEntity(f.getType(), subEntityUuid));
+            ReflectionUtils.setField(f, target, fetchEntity(namePrefix + f.getName() + ".uuid", f.getType(), subEntityUuid));
         }
         return target;
     }
@@ -82,13 +86,15 @@ abstract class Mapper extends ModelMapper {
             .toArray(Field[]::new);
     }
 
-    public <E> E fetchEntity(final Class<E> entityClass, final Object subEntityUuid) {
-        // using getReference would be more efficent, but results in very technical error messages
+    public <E> E fetchEntity(final String propertyName, final Class<E> entityClass, final Object subEntityUuid) {
+        // using getReference would be more efficient, but results in very technical error messages
         final var entity = em.find(entityClass, subEntityUuid); // FIXME: try getReference
         if (entity != null) {
             return entity;
         }
-        throw new ValidationException("Unable to find " + DisplayName.of(entityClass) + " by uuid: " + subEntityUuid);
+        throw new ValidationException(
+                "Unable to find " + DisplayName.of(entityClass) +
+                " by " + propertyName + ": " + subEntityUuid);
     }
 
     public <S, T> T map(final S source, final Class<T> targetClass, final BiConsumer<S, T> postMapper) {
@@ -99,4 +105,13 @@ abstract class Mapper extends ModelMapper {
         postMapper.accept(source, target);
         return target;
     }
+
+    public <S, T> T map(final String namePrefix, final S source, final Class<T> targetClass, final BiConsumer<S, T> postMapper) {
+        if (source == null) {
+            return null;
+        }
+        final var target = map(source, targetClass);
+        postMapper.accept(source, target);
+        return target;
+    }
 }
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java
index 98ba650c..7f3b2281 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java
@@ -405,7 +405,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
                     .post("http://localhost/api/hs/office/debitors")
                 .then().log().all().assertThat()
                     .statusCode(400)
-                    .body("message", is("ERROR: [400] Unable to find RealContact by debitorRel.contactUuid: 00000000-0000-0000-0000-000000000000"));
+                    .body("message", is("ERROR: [400] Unable to find RealContact by debitorRel.contact.uuid: 00000000-0000-0000-0000-000000000000"));
             // @formatter:on
         }
 
@@ -433,7 +433,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
                     .post("http://localhost/api/hs/office/debitors")
                 .then().log().all().assertThat()
                     .statusCode(400)
-                    .body("message", is("ERROR: [400] Unable to find RealRelation by uuid: 00000000-0000-0000-0000-000000000000"));
+                    .body("message", is("ERROR: [400] Unable to find RealRelation by debitorRel.uuid: 00000000-0000-0000-0000-000000000000"));
                 // @formatter:on
         }
     }