diff --git a/src/bloxel/storage/bloxel_array.rs b/src/bloxel/storage/bloxel_array.rs
index 7484068..b07a2c4 100644
--- a/src/bloxel/storage/bloxel_array.rs
+++ b/src/bloxel/storage/bloxel_array.rs
@@ -23,7 +23,7 @@ impl<T: Copy> BloxelArray<T> {
         Self { size, data }
     }
 
-    pub fn from_fn(size: USize3, f: impl Fn(IVec3) -> T) -> Self {
+    pub fn from_fn(size: USize3, mut f: impl FnMut(IVec3) -> T) -> Self {
         let f = |(x, y, z)| f(IVec3::new(x as i32, y as i32, z as i32));
         let data = Array3::from_shape_fn(size, f);
         Self { size, data }
diff --git a/src/bloxel/storage/bloxel_store.rs b/src/bloxel/storage/bloxel_store.rs
index abe0a42..3c49417 100644
--- a/src/bloxel/storage/bloxel_store.rs
+++ b/src/bloxel/storage/bloxel_store.rs
@@ -12,7 +12,7 @@ pub trait BloxelStore<T: Copy> {
 pub trait BloxelStoreMut<T: Copy>: BloxelStore<T> {
     fn set(&mut self, pos: IVec3, value: T) -> Result<T, ()>;
 
-    fn update(&mut self, f: impl Fn(IVec3, T) -> T) {
+    fn update(&mut self, mut f: impl FnMut(IVec3, T) -> T) {
         let (w, h, d) = self.size().into();
         for prod in Hom3FCartProd::new(0..w, 0..h, 0..d) {
             let pos = UVec3::from(prod).as_ivec3();