diff --git a/src/pydase/data_service/data_service.py b/src/pydase/data_service/data_service.py
index 36d45e5..06dd197 100644
--- a/src/pydase/data_service/data_service.py
+++ b/src/pydase/data_service/data_service.py
@@ -83,8 +83,9 @@ class DataService(rpyc.Service, AbstractDataService):
 
     def __check_instance_classes(self) -> None:
         for attr_name, attr_value in get_class_and_instance_attributes(self).items():
-            # every class defined by the user should inherit from DataService
-            if not attr_name.startswith("_DataService__"):
+            # every class defined by the user should inherit from DataService if it is
+            # assigned to a public attribute
+            if not attr_name.startswith("_"):
                 warn_if_instance_class_does_not_inherit_from_DataService(attr_value)
 
     def __set_attribute_based_on_type(  # noqa:CFQ002
diff --git a/tests/test_warnings.py b/tests/utils/test_warnings.py
similarity index 67%
rename from tests/test_warnings.py
rename to tests/utils/test_warnings.py
index aae794b..8bd5922 100644
--- a/tests/test_warnings.py
+++ b/tests/utils/test_warnings.py
@@ -2,7 +2,7 @@ from pytest import LogCaptureFixture
 
 from pydase import DataService
 
-from . import caplog  # noqa
+from .. import caplog  # noqa
 
 
 def test_setattr_warnings(caplog: LogCaptureFixture) -> None:  # noqa
@@ -32,3 +32,19 @@ def test_private_attribute_warning(caplog: LogCaptureFixture) -> None:  # noqa
         " Warning: You should not set private but rather protected attributes! Use "
         "_something instead of __something." in caplog.text
     )
+
+
+def test_protected_attribute_warning(caplog: LogCaptureFixture) -> None:  # noqa
+    class SubClass:
+        name = "Hello"
+
+    class ServiceClass(DataService):
+        def __init__(self) -> None:
+            self._subclass = SubClass
+            super().__init__()
+
+    ServiceClass()
+
+    assert (
+        "Warning: Class SubClass does not inherit from DataService." not in caplog.text
+    )