diff --git a/src/pydase/data_service/data_service.py b/src/pydase/data_service/data_service.py
index 7a7c2bd..2e6a587 100644
--- a/src/pydase/data_service/data_service.py
+++ b/src/pydase/data_service/data_service.py
@@ -70,6 +70,11 @@ class DataService(rpyc.Service, AbstractDataService):
         # Warn if setting private attributes
         self._warn_on_private_attr_set(__name)
 
+        # every class defined by the user should inherit from DataService if it is
+        # assigned to a public attribute
+        if not __name.startswith("_"):
+            warn_if_instance_class_does_not_inherit_from_data_service(__value)
+
         # Set the attribute
         super().__setattr__(__name, __value)
 
diff --git a/src/pydase/utils/warnings.py b/src/pydase/utils/warnings.py
index 500be15..2e9cb30 100644
--- a/src/pydase/utils/warnings.py
+++ b/src/pydase/utils/warnings.py
@@ -22,6 +22,7 @@ def warn_if_instance_class_does_not_inherit_from_data_service(__value: object) -
         and type(__value).__name__ not in ["CallbackManager", "TaskManager", "Quantity"]
     ):
         logger.warning(
-            "Warning: Class '%s' does not inherit from DataService.",
+            "Class '%s' does not inherit from DataService. This may lead to unexpected "
+            "behaviour!",
             type(__value).__name__,
         )
diff --git a/tests/utils/test_warnings.py b/tests/utils/test_warnings.py
index b251749..0abca37 100644
--- a/tests/utils/test_warnings.py
+++ b/tests/utils/test_warnings.py
@@ -2,8 +2,22 @@ from pydase import DataService
 from pytest import LogCaptureFixture
 
 
-def test_setattr_warnings(caplog: LogCaptureFixture) -> None:
-    # def test_setattr_warnings(capsys: CaptureFixture) -> None:
+def test_class_attr_inheritance_warning(caplog: LogCaptureFixture) -> None:
+    class SubClass:
+        name = "Hello"
+
+    class ServiceClass(DataService):
+        attr_1 = SubClass()
+
+    ServiceClass()
+
+    assert (
+        "Class 'SubClass' does not inherit from DataService. This may lead to "
+        "unexpected behaviour!"
+    ) in caplog.text
+
+
+def test_instance_attr_inheritance_warning(caplog: LogCaptureFixture) -> None:
     class SubClass:
         name = "Hello"
 
@@ -14,7 +28,10 @@ def test_setattr_warnings(caplog: LogCaptureFixture) -> None:
 
     ServiceClass()
 
-    assert "Warning: Class 'SubClass' does not inherit from DataService." in caplog.text
+    assert (
+        "Class 'SubClass' does not inherit from DataService. This may lead to "
+        "unexpected behaviour!"
+    ) in caplog.text
 
 
 def test_private_attribute_warning(caplog: LogCaptureFixture) -> None: