diff --git a/deepxde/data/pde_operator.py b/deepxde/data/pde_operator.py
index 035091817..d3f6cc1ec 100644
--- a/deepxde/data/pde_operator.py
+++ b/deepxde/data/pde_operator.py
@@ -281,7 +281,6 @@ def forward_call(trunk_input):
                 f = self.pde.pde(inputs[1], (outputs, forward_call), model.net.auxiliary_vars)
                 if not isinstance(f, (list, tuple)):
                     f = [f]
-            bcs_start = np.cumsum([0] + self.pde.num_bcs)
             error_f = [fi[:, bcs_start[-1]:] for fi in f]
             losses = [loss_fn(bkd.zeros_like(error), error) for error in error_f]  # noqa
             # BC