diff --git a/grudge/symbolic/operators.py b/grudge/symbolic/operators.py
index 5f5cd5c9e0d6c7cc895db68f4110ff8a74d63e15..9b6fd75806d6ed69c6188ca8bd13f184f218e955 100644
--- a/grudge/symbolic/operators.py
+++ b/grudge/symbolic/operators.py
@@ -154,6 +154,7 @@ class InterpolationOperator(Operator):
         def interp_one(subexpr):
             from pymbolic.primitives import is_constant
             if self.dd_in == self.dd_out:
+                # no-op interpolation, go away
                 return subexpr
             elif is_constant(subexpr):
                 return subexpr