diff --git a/deepxde/data/pde_operator.py b/deepxde/data/pde_operator.py
index cca1b15a0..8d0bf97c1 100644
--- a/deepxde/data/pde_operator.py
+++ b/deepxde/data/pde_operator.py
@@ -267,7 +267,7 @@ def forward_call(trunk_input):
                 return aux[0]((inputs[0], trunk_input))
 
             if self.pde.pde is not None:
-                # Each f has the shape (`N1`, `N2`)
+                # Each f has the shape (N1, N2)
                 f = self.pde.pde(
                     inputs[1], (outputs, forward_call), model.net.auxiliary_vars
                 )