diff --git a/mex/common/models/base.py b/mex/common/models/base.py
index 10e709e5..a6475550 100644
--- a/mex/common/models/base.py
+++ b/mex/common/models/base.py
@@ -185,8 +185,15 @@ def verify_computed_field_consistency(
             data with consistent computed fields.
         """
         if not cls.model_computed_fields:
+            # no computed fields: exit early
+            return handler(data)
+        if isinstance(data, cls):
+            # data is a model instance: we can assume no computed field was set,
+            # because pydantic would throw an AttributeError if you tried
             return handler(data)
         if not isinstance(data, MutableMapping):
+            # data is not a dictionary: we can't "pop" values from that,
+            # so we can't safely do a before/after comparison
             raise AssertionError(
                 "Input should be a valid dictionary, validating other types is not "
                 "supported for models with computed fields."
diff --git a/mex/common/organigram/transform.py b/mex/common/organigram/transform.py
index 5e0defcf..2ee60da5 100644
--- a/mex/common/organigram/transform.py
+++ b/mex/common/organigram/transform.py
@@ -48,14 +48,7 @@ def transform_organigram_units_to_organizational_units(
             if parent_unit := extracted_unit_by_id_in_primary_source.get(
                 parent_identifier_in_primary_source
             ):
-                # Create a copy, because extracted data instances are immutable
-                # because of `BaseEntity.verify_computed_field_consistency`
-                extracted_unit = ExtractedOrganizationalUnit.model_validate(
-                    {
-                        **extracted_unit.model_dump(),
-                        "parentUnit": MergedOrganizationalUnitIdentifier(
-                            parent_unit.stableTargetId
-                        ),
-                    }
+                extracted_unit.parentUnit = MergedOrganizationalUnitIdentifier(
+                    parent_unit.stableTargetId
                 )
         yield extracted_unit
diff --git a/tests/models/test_base.py b/tests/models/test_base.py
index 622679ba..71157c29 100644
--- a/tests/models/test_base.py
+++ b/tests/models/test_base.py
@@ -89,13 +89,17 @@ class Shelter(Pet):
         Shelter(inhabitants="foo")  # type: ignore
 
 
-def test_verify_computed_field_consistency() -> None:
-    class Computer(BaseModel):
+class Computer(BaseModel):
+
+    ram: int = 16
+
+    @computed_field  # type: ignore[misc]
+    @property
+    def cpus(self) -> int:
+        return 42
 
-        @computed_field  # type: ignore[misc]
-        @property
-        def cpus(self) -> int:
-            return 42
+
+def test_verify_computed_field_consistency() -> None:
 
     computer = Computer.model_validate({"cpus": 42})
     assert computer.cpus == 42
@@ -105,7 +109,7 @@ def cpus(self) -> int:
         match="Input should be a valid dictionary, validating other types is not "
         "supported for models with computed fields.",
     ):
-        Computer.model_validate(computer)
+        Computer.model_validate('{"cpus": 1}')
 
     with pytest.raises(ValidationError, match="Cannot set computed fields"):
         Computer.model_validate({"cpus": 1})
@@ -114,6 +118,19 @@ def cpus(self) -> int:
         Computer(cpus=99)
 
 
+def test_field_assignment_on_model_with_computed_field() -> None:
+    computer = Computer()
+
+    # computed field cannot be set
+    with pytest.raises(
+        AttributeError, match="property 'cpus' of 'Computer' object has no setter"
+    ):
+        computer.cpus = 99
+
+    # non-computed field works as expected
+    computer.ram = 32
+
+
 class DummyBaseModel(BaseModel):
     foo: str | None = None