diff --git a/multigrid/src/main.rs b/multigrid/src/main.rs
index 4f2684f..bfda683 100644
--- a/multigrid/src/main.rs
+++ b/multigrid/src/main.rs
@@ -105,21 +105,19 @@ impl System {
     }
 
     fn advance(&mut self, dt: Float, pool: &rayon::ThreadPool) {
-        type MT<'a> = (
-            &'a mut [euler::WorkBuffers],
-            &'a mut [euler::BoundaryStorage],
-        );
         let metrics = &self.metrics;
+        let grids = &self.grids;
+        let bt = &self.bt;
+        let wb = &mut self.wb;
+        let mut eb = &mut self.eb;
+
         let rhs = move |fut: &mut [euler::Field],
                         prev: &[euler::Field],
                         time: Float,
-                        c: &(&[grid::Grid], &[euler::BoundaryCharacteristics]),
-                        mt: &mut MT| {
-            let (grids, bt) = c;
-            let (wb, eb) = mt;
-
+                        _c: (),
+                        _mt: &mut ()| {
             let bc = euler::extract_boundaries::<operators::Interpolation4>(
-                prev, *bt, *eb, *grids, time,
+                prev, &bt, &mut eb, &grids, time,
             );
             pool.scope(|s| {
                 for ((((fut, prev), bc), wb), metrics) in fut
@@ -168,8 +166,8 @@ impl System {
             &mut self.time,
             dt,
             &mut k,
-            &(&self.grids, &self.bt),
-            &mut (&mut self.wb, &mut self.eb),
+            (),
+            &mut (),
             pool,
         );
 
diff --git a/sbp/src/integrate.rs b/sbp/src/integrate.rs
index 0b7fe31..c11e8b3 100644
--- a/sbp/src/integrate.rs
+++ b/sbp/src/integrate.rs
@@ -89,7 +89,7 @@ impl ButcherTableau for Rk6 {
 
 #[allow(clippy::too_many_arguments)]
 pub fn integrate<'a, BTableau, F: 'a, RHS, MT, C>(
-    rhs: RHS,
+    mut rhs: RHS,
     prev: &F,
     fut: &mut F,
     time: &mut Float,
@@ -101,7 +101,7 @@ pub fn integrate<'a, BTableau, F: 'a, RHS, MT, C>(
 ) where
     C: Copy,
     F: std::ops::Deref<Target = Array3<Float>> + std::ops::DerefMut<Target = Array3<Float>>,
-    RHS: Fn(&mut F, &F, Float, C, &mut MT),
+    RHS: FnMut(&mut F, &F, Float, C, &mut MT),
     BTableau: ButcherTableau,
 {
     assert_eq!(prev.shape(), fut.shape());
@@ -147,7 +147,7 @@ pub fn integrate<'a, BTableau, F: 'a, RHS, MT, C>(
 #[cfg(feature = "rayon")]
 #[allow(clippy::too_many_arguments)]
 pub fn integrate_multigrid<'a, BTableau, F: 'a, RHS, MT, C>(
-    rhs: RHS,
+    mut rhs: RHS,
     prev: &[F],
     fut: &mut [F],
     time: &mut Float,
@@ -163,7 +163,7 @@ pub fn integrate_multigrid<'a, BTableau, F: 'a, RHS, MT, C>(
         + std::ops::DerefMut<Target = Array3<Float>>
         + Send
         + Sync,
-    RHS: Fn(&mut [F], &[F], Float, C, &mut MT),
+    RHS: FnMut(&mut [F], &[F], Float, C, &mut MT),
     BTableau: ButcherTableau,
 {
     for i in 0.. {