diff --git a/deepxde/data/pde_operator.py b/deepxde/data/pde_operator.py
index 1b9cda494..50a97b27f 100644
--- a/deepxde/data/pde_operator.py
+++ b/deepxde/data/pde_operator.py
@@ -242,6 +242,7 @@ def _losses(self, outputs, loss_fn, inputs, model, num_func, aux=None):
 
         if config.autodiff == "forward": # forward mode AD
             losses=[]
+
             def forward_call(trunk_input):
                 return aux[0]((inputs[0], trunk_input))