diff --git a/optimum/onnxruntime/modeling_diffusion.py b/optimum/onnxruntime/modeling_diffusion.py
index 14e41f27818..bf6dc002f9e 100644
--- a/optimum/onnxruntime/modeling_diffusion.py
+++ b/optimum/onnxruntime/modeling_diffusion.py
@@ -560,7 +560,7 @@ def prepare_onnx_outputs(
 
     @abstractmethod
     def forward(self, *args, **kwargs):
-        pass
+        raise NotImplementedError
 
     def __call__(self, *args, **kwargs):
         return self.forward(*args, **kwargs)