diff --git a/experiments/volume_potential_3d_derivatives.py b/experiments/volume_potential_3d_derivatives.py
index 023871c27bc4e7b42975179e6110db48c897eed8..db78c3a98201fa6509e9f6e92802db78e27db31d 100644
--- a/experiments/volume_potential_3d_derivatives.py
+++ b/experiments/volume_potential_3d_derivatives.py
@@ -323,9 +323,11 @@ local_expn_class = expn_factory.get_local_expansion_class(knl)
 mpole_expn_class = expn_factory.get_multipole_expansion_class(knl)
 
 exclude_self = True
-from volumential.expansion_wrangler_interface import ExpansionWranglerCodeContainer
+from volumential.expansion_wrangler_fpnd import (
+        FPNDExpansionWranglerCodeContainer,
+        FPNDExpansionWrangler)
 
-wcc = ExpansionWranglerCodeContainer(
+wcc = FPNDExpansionWranglerCodeContainer(
     ctx,
     partial(mpole_expn_class, knl),
     partial(local_expn_class, knl),
@@ -339,8 +341,6 @@ if exclude_self:
 else:
     self_extra_kwargs = {}
 
-from volumential.expansion_wrangler_fpnd import FPNDExpansionWrangler
-
 wrangler = FPNDExpansionWrangler(
     code_container=wcc,
     queue=queue,
diff --git a/test/test_interpolation.py b/test/test_interpolation.py
index 07fffa73b3088c41600b3295508a7d5e34c25159..bcc74a483bd74c38374567151752b5c48629ab85 100644
--- a/test/test_interpolation.py
+++ b/test/test_interpolation.py
@@ -50,8 +50,10 @@ def random_polynomial_func(dim, degree, seed=None):
         npts = pts.shape[1]
         res = np.zeros(npts)
         for deg in np.ndindex(coefs.shape):
+            mono = np.ones(npts)
             for iaxis in range(dim):
-                res += coefs[deg] * pts[iaxis, :]**deg[iaxis]
+                mono += pts[iaxis, :]**deg[iaxis]
+            res += coefs[deg] * mono
         return res
 
     return poly_func
diff --git a/volumential/tools.py b/volumential/tools.py
index 6b24224c3fa917746b7a8d651a4287b92c604486..146c6e1f1d8d8ccb47ab6bba3a68b248956e60af 100644
--- a/volumential/tools.py
+++ b/volumential/tools.py
@@ -496,14 +496,13 @@ class DiscreteLegendreTransform(BoxSpecificMap):
         """
 
         if filtering is None:
-            filter_multiplier = 1 + cl.array.zeros(queue,
-                    self.degree**self.dim, np.float64)
+            filter_multiplier = 1 + cl.array.zeros(
+                queue, self.degree**self.dim, np.float64)
         elif isinstance(filtering, cl.array.Array):
             assert filtering.shape == (self.degree**self.dim,)
             filter_multiplier = filtering
         else:
-            raise RuntimeError("Invalid filtering argument: %s"
-                    % str(filtering))
+            raise RuntimeError(f"Invalid filtering argument: {str(filtering)}")
 
         knl = self.get_cached_optimized_kernel()
 
@@ -528,6 +527,18 @@ class DiscreteLegendreTransform(BoxSpecificMap):
 
 # }}} End discrete Legendre transform
 
+# {{{ inverse discrete Legendre transform
+
+
+class InverseDiscreteLegendreTransform(BoxSpecificMap):
+    """
+    Box-specific transform that maps box-local modal coefficients
+    to nodal values. Inverse of :class:`DiscreteLegendreTransform`.
+    """
+    pass
+
+# }}} End inverse discrete Legendre transform
+
 # }}} End box-specific maps
 
 # {{{ box-specific reductions