diff --git a/sbp/src/operators/interpolation.rs b/sbp/src/operators/interpolation.rs
index 3b1aa5e..c69d834 100644
--- a/sbp/src/operators/interpolation.rs
+++ b/sbp/src/operators/interpolation.rs
@@ -55,7 +55,7 @@ pub(crate) fn test_interpolation_operator<IO: InterpolationOperator>(op: IO, h2:
     let (x_c, x_f) = if h2 {
         (
             crate::utils::h2linspace(0.0, 1.0, nc),
-            crate::utils::h2linspace(0.0, 1.0, 2 * nc - 1),
+            crate::utils::h2linspace(0.0, 1.0, 2 * (nc - 1)),
         )
     } else {
         (
@@ -66,9 +66,9 @@ pub(crate) fn test_interpolation_operator<IO: InterpolationOperator>(op: IO, h2:
 
     let mut ix_f = ndarray::Array1::zeros(x_f.raw_dim());
     op.coarse2fine(x_c.view(), ix_f.view_mut());
-    approx::assert_abs_diff_eq!(ix_f, x_f, epsilon = 1e-2);
+    approx::assert_abs_diff_eq!(ix_f, x_f, epsilon = 1e-5);
 
     let mut ix_c = ndarray::Array1::zeros(x_c.raw_dim());
     op.fine2coarse(x_f.view(), ix_c.view_mut());
-    approx::assert_abs_diff_eq!(ix_c, x_c, epsilon = 1e-2);
+    approx::assert_abs_diff_eq!(ix_c, x_c, epsilon = 1e-5);
 }
diff --git a/sbp/src/operators/interpolation/interpolation9h2.rs b/sbp/src/operators/interpolation/interpolation9h2.rs
index 9a3b395..f1ee50d 100644
--- a/sbp/src/operators/interpolation/interpolation9h2.rs
+++ b/sbp/src/operators/interpolation/interpolation9h2.rs
@@ -51,7 +51,7 @@ impl Interpolation9h2 {
 
 impl InterpolationOperator for Interpolation9h2 {
     fn fine2coarse(&self, fine: ArrayView1<Float>, coarse: ArrayViewMut1<Float>) {
-        assert_eq!(fine.len(), 2 * coarse.len() - 1);
+        assert_eq!(fine.len(), 2 * (coarse.len() - 1));
         use ndarray::prelude::*;
         use std::iter::FromIterator;
         let block = Array::from_iter(Self::F2C_BLOCK.iter().flatten().copied())
@@ -63,7 +63,7 @@ impl InterpolationOperator for Interpolation9h2 {
         super::interpolate(fine, coarse, block.view(), diag.view(), (4, 2))
     }
     fn coarse2fine(&self, coarse: ArrayView1<Float>, fine: ArrayViewMut1<Float>) {
-        assert_eq!(fine.len(), 2 * coarse.len() - 1);
+        assert_eq!(fine.len(), 2 * (coarse.len() - 1));
         use ndarray::prelude::*;
         use std::iter::FromIterator;
         let block = Array::from_iter(Self::C2F_BLOCK.iter().flatten().copied())