diff --git a/src/computed.ts b/src/computed.ts
index 2848fbb..8013e77 100644
--- a/src/computed.ts
+++ b/src/computed.ts
@@ -13,37 +13,35 @@ export type ComputedStateCreator = <
   Mps extends [StoreMutatorIdentifier, unknown][] = [],
   Mcs extends [StoreMutatorIdentifier, unknown][] = [],
 >(
+  compute: (state: T) => A,
   f: StateCreator<T, [...Mps, ["chrisvander/zustand-computed", A]], Mcs>,
+  opts?: ComputedStateOpts<T>,
+) => StateCreator<T, Mps, [["chrisvander/zustand-computed", A], ...Mcs], T>
+
+type ComputedStateImpl = <T extends object, A extends object>(
   compute: (state: T) => A,
+  f: StateCreator<T, [], []>,
   opts?: ComputedStateOpts<T>,
-) => StateCreator<T, Mps, [["chrisvander/zustand-computed", A], ...Mcs], T & A>
+) => StateCreator<T, [], [], T>
 
-type Cast<T, U> = T extends U ? T : U
 type Write<T, U> = Omit<T, keyof U> & U
 type StoreCompute<S, A> = S extends {
   getState: () => infer T
 }
-  ? Omit<StoreApi<T & A>, "setState">
+  ? Omit<StoreApi<T & Readonly<A>>, "setState" | "getInitialState">
   : never
-type WithCompute<S, A> = Write<S, StoreCompute<S, A>>
 
 declare module "zustand" {
   interface StoreMutators<S, A> {
-    "chrisvander/zustand-computed": WithCompute<Cast<S, object>, A>
+    "chrisvander/zustand-computed": Write<S, StoreCompute<S, A>>
   }
 }
 
-type ComputedStateImpl = <T extends object, A extends object>(
-  f: StateCreator<T, [], []>,
-  compute: (state: T) => A,
-  opts?: ComputedStateOpts<T>,
-) => StateCreator<T, [], [], T & A>
-
 type SetStateWithArgs = Parameters<ReturnType<ComputedStateImpl>>[0] extends (...args: infer U) => void
   ? (...args: [...U, ...unknown[]]) => void
   : never
 
-const computedImpl: ComputedStateImpl = (f, compute, opts) => {
+const computedImpl: ComputedStateImpl = (compute, f, opts) => {
   // set of keys that have been accessed in any compute call
   const trackedSelectors = new Set<string | number | symbol>()
   return (set, get, api) => {