diff --git a/grudge/function_registry.py b/grudge/function_registry.py
index 2f56eba4ad26d066039f5ac373619ac4ac10a656..4d521560d8e6c83a8e9fa238b3c46955dc62e7a7 100644
--- a/grudge/function_registry.py
+++ b/grudge/function_registry.py
@@ -136,6 +136,7 @@ class CElementwiseBinaryFunction(Function):
             return func(arg0, arg1)
 
         from pymbolic.primitives import Variable
+
         @memoize_in(self, "map_call_knl_%s" % func_name)
         def knl():
             i = Variable("i")
diff --git a/grudge/symbolic/operators.py b/grudge/symbolic/operators.py
index c1360b1627a79ccafe3e52405a099f550012a410..9b6fd75806d6ed69c6188ca8bd13f184f218e955 100644
--- a/grudge/symbolic/operators.py
+++ b/grudge/symbolic/operators.py
@@ -146,15 +146,23 @@ class ElementwiseLinearOperator(Operator):
 
 class InterpolationOperator(Operator):
     def __init__(self, dd_in, dd_out):
-        import grudge.symbolic.primitives as prim
-        official_dd_in = prim.as_dofdesc(dd_in)
-        official_dd_out = prim.as_dofdesc(dd_out)
+        super(InterpolationOperator, self).__init__(dd_in, dd_out)
 
-        if official_dd_in == official_dd_out:
-            raise ValueError("Interpolating from {} to {}"
-            " does not do anything.".format(official_dd_in, official_dd_out))
+    def __call__(self, expr):
+        from pytools.obj_array import with_object_array_or_scalar
 
-        super(InterpolationOperator, self).__init__(dd_in, dd_out)
+        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
+            else:
+                from grudge.symbolic.primitives import OperatorBinding
+                return OperatorBinding(self, subexpr)
+
+        return with_object_array_or_scalar(interp_one, expr)
 
     mapper_method = intern("map_interpolation")