diff --git a/crates/types/src/compound/enumerated.rs b/crates/types/src/compound/enumerated.rs
index 18df3dc..32725c5 100644
--- a/crates/types/src/compound/enumerated.rs
+++ b/crates/types/src/compound/enumerated.rs
@@ -60,20 +60,20 @@ pub trait DiscrHandler<N: Peano, R> {
 }
 
 /// helper used to call F with some (yet-to-be-determined) index of I
-struct DispatchIndexable<'a, I, F> {
-    indexable: &'a I,
+struct DispatchIndexable<I, F> {
+    indexable: I,
     f: F,
 }
 
-impl<'a, I, F> DispatchIndexable<'a, I, F> {
-    fn new(indexable: &'a I, f: F) -> Self {
+impl<I, F> DispatchIndexable<I, F> {
+    fn new(indexable: I, f: F) -> Self {
         Self { indexable, f }
     }
 }
 
 // base case: we tried to index all cases >= 0 and failed.
 // this should be unreachable.
-impl<'a, I, F, R> DiscrHandler<P0, R> for DispatchIndexable<'a, I, F>
+impl<'a, I, F, R> DiscrHandler<P0, R> for DispatchIndexable<I, F>
 {
     type PrevOrPanic = Self;
     fn call(self) -> R {
@@ -86,7 +86,7 @@ impl<'a, I, F, R> DiscrHandler<P0, R> for DispatchIndexable<'a, I, F>
 
 // inductive case: if we know how dispatch up through P, and the collection is P+1-indexable, then we can
 // index up through P+1
-impl<'a, I, F, P: Peano, R> DiscrHandler<PNext<P>, R> for DispatchIndexable<'a, I, F>
+impl<'a, I, F, P: Peano, R> DiscrHandler<PNext<P>, R> for DispatchIndexable<&'a I, F>
 where
     I: Indexable<P>,
     I::Element: Copy,
@@ -102,6 +102,24 @@ where
     }
 }
 
+// mutable indexing case: if we have a mutable handle to the Indexable,
+// then assume the variants want to have mutable references to the items.
+impl<'a, I, F, P: Peano, R> DiscrHandler<PNext<P>, R> for DispatchIndexable<&'a mut I, F>
+where
+    I: Indexable<P>,
+    I::Element: 'a,
+    F: VariantHandler<P, &'a mut I::Element, R>,
+    Self: DiscrHandler<P, R>,
+{
+    type PrevOrPanic = Self;
+    fn call(self) -> R {
+        self.f.call(self.indexable.get_mut())
+    }
+    fn prev(self) -> Self::PrevOrPanic {
+        self
+    }
+}
+
 #[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]
 #[cfg_attr(feature = "fmt", derive(Debug))]
 #[derive(Copy, Clone, Default, PartialEq)]
@@ -145,35 +163,64 @@ where
 impl<D, L> Enum<D, L>
 where Self: EnumRequirements
 {
+    /// invoke the closure on the active variant, passing the variant by-value
     fn dispatch<'a, F, R>(&'a self, f: F) -> R
     where
-        DispatchIndexable<'a, L, F>: DiscrHandler<<Self as EnumRequirements>::NumVariants, R>
+        DispatchIndexable<&'a L, F>: DiscrHandler<<Self as EnumRequirements>::NumVariants, R>
     {
         self.decode_discr().dispatch(DispatchIndexable::new(&self.1, f))
     }
+
+    /// invoke the closure on the active variant, passing the variant by mutable reference
+    fn dispatch_mut<'a, F, R>(&'a mut self, f: F) -> R
+    where
+        DispatchIndexable<&'a mut L, F>: DiscrHandler<<Self as EnumRequirements>::NumVariants, R>
+    {
+        self.decode_discr().dispatch(DispatchIndexable::new(&mut self.1, f))
+    }
 }
 
 #[cfg(test)]
 mod test {
     use super::*;
-    #[test]
-    fn dispatch() {
-        struct Receiver;
-        impl<P: Peano, T: TryInto<i32>> VariantHandler<P, T, i32> for Receiver {
-            fn call(&self, v: T) -> i32 {
-                unsafe {
-                    v.try_into().unwrap_unchecked() + P::VALUE as i32 + 5
-                }
+
+    struct ImmutableReceiver;
+    impl<P: Peano, T: TryInto<i32>> VariantHandler<P, T, i32> for ImmutableReceiver {
+        fn call(&self, v: T) -> i32 {
+            unsafe {
+                v.try_into().unwrap_unchecked() + P::VALUE as i32 + 5
             }
         }
+    }
 
+    struct Add4Receiver;
+    impl<P: Peano, T: TryInto<i32> + TryFrom<i32> + Copy> VariantHandler<P, &mut T, ()> for Add4Receiver {
+        fn call(&self, v: &mut T) -> () {
+            unsafe {
+                *v = ((*v).try_into().unwrap_unchecked() + 4).try_into().unwrap_unchecked();
+            }
+        }
+    }
+
+    #[test]
+    fn dispatch() {
         let mut e: Enum<(Discr<P3>,), List<(u32, i32, u8)>> = Enum::default();
-        assert_eq!(e.dispatch(Receiver), 5);
+        assert_eq!(e.dispatch(ImmutableReceiver), 5);
 
         e.encode_discr(Discr::new(1));
-        assert_eq!(e.dispatch(Receiver), 6);
+        assert_eq!(e.dispatch(ImmutableReceiver), 6);
 
         e.encode_discr(Discr::new(2));
-        assert_eq!(e.dispatch(Receiver), 7);
+        assert_eq!(e.dispatch(ImmutableReceiver), 7);
+    }
+
+    #[test]
+    fn dispatch_mut() {
+        let mut e: Enum<(Discr<P3>,), List<(u32, i32, u8)>> = Enum::default();
+        e.dispatch_mut(Add4Receiver);
+        assert_eq!(e.dispatch(ImmutableReceiver), 9);
+
+        e.encode_discr(Discr::new(1));
+        assert_eq!(e.dispatch(ImmutableReceiver), 6);
     }
 }