diff --git a/src/createStore.ts b/src/createStore.ts
index 2560ad863e..9e13aa2291 100644
--- a/src/createStore.ts
+++ b/src/createStore.ts
@@ -6,7 +6,6 @@ import {
   StoreEnhancer,
   Dispatch,
   Observer,
-  ExtendState,
   ListenerCallback
 } from './types/store'
 import { Action } from './types/actions'
@@ -43,7 +42,7 @@ import { kindOf } from './utils/kindOf'
 export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
   reducer: Reducer<S, A>,
   enhancer?: StoreEnhancer<Ext, StateExt>
-): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+): Store<S, A, StateExt> & Ext
 /**
  * @deprecated
  *
@@ -73,12 +72,12 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
   reducer: Reducer<S, A>,
   preloadedState?: PreloadedState<S>,
   enhancer?: StoreEnhancer<Ext, StateExt>
-): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+): Store<S, A, StateExt> & Ext
 export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
   reducer: Reducer<S, A>,
   preloadedState?: PreloadedState<S> | StoreEnhancer<Ext, StateExt>,
   enhancer?: StoreEnhancer<Ext, StateExt>
-): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext {
+): Store<S, A, StateExt> & Ext {
   if (typeof reducer !== 'function') {
     throw new Error(
       `Expected the root reducer to be a function. Instead, received: '${kindOf(
@@ -115,7 +114,7 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
     return enhancer(createStore)(
       reducer,
       preloadedState as PreloadedState<S>
-    ) as Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+    ) as Store<S, A, StateExt> & Ext
   }
 
   let currentReducer = reducer
@@ -291,11 +290,8 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
    * implement a hot reloading mechanism for Redux.
    *
    * @param nextReducer The reducer for the store to use instead.
-   * @returns The same store instance with a new reducer in place.
    */
-  function replaceReducer<NewState, NewActions extends A>(
-    nextReducer: Reducer<NewState, NewActions>
-  ): Store<ExtendState<NewState, StateExt>, NewActions, StateExt, Ext> & Ext {
+  function replaceReducer(nextReducer: Reducer<S, A>): void {
     if (typeof nextReducer !== 'function') {
       throw new Error(
         `Expected the nextReducer to be a function. Instead, received: '${kindOf(
@@ -304,22 +300,13 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
       )
     }
 
-    // TODO: do this more elegantly
-    ;(currentReducer as unknown as Reducer<NewState, NewActions>) = nextReducer
+    currentReducer = nextReducer
 
     // This action has a similar effect to ActionTypes.INIT.
     // Any reducers that existed in both the new and old rootReducer
     // will receive the previous state. This effectively populates
     // the new state tree with any relevant data from the old one.
     dispatch({ type: ActionTypes.REPLACE } as A)
-    // change the type of the store by casting it to the new store
-    return store as unknown as Store<
-      ExtendState<NewState, StateExt>,
-      NewActions,
-      StateExt,
-      Ext
-    > &
-      Ext
   }
 
   /**
@@ -377,7 +364,7 @@ export function createStore<S, A extends Action, Ext = {}, StateExt = never>(
     getState,
     replaceReducer,
     [$$observable]: observable
-  } as unknown as Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+  } as unknown as Store<S, A, StateExt> & Ext
   return store
 }
 
@@ -419,7 +406,7 @@ export function legacy_createStore<
 >(
   reducer: Reducer<S, A>,
   enhancer?: StoreEnhancer<Ext, StateExt>
-): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+): Store<S, A, StateExt> & Ext
 /**
  * Creates a Redux store that holds the state tree.
  *
@@ -459,7 +446,7 @@ export function legacy_createStore<
   reducer: Reducer<S, A>,
   preloadedState?: PreloadedState<S>,
   enhancer?: StoreEnhancer<Ext, StateExt>
-): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+): Store<S, A, StateExt> & Ext
 export function legacy_createStore<
   S,
   A extends Action,
@@ -469,6 +456,6 @@ export function legacy_createStore<
   reducer: Reducer<S, A>,
   preloadedState?: PreloadedState<S> | StoreEnhancer<Ext, StateExt>,
   enhancer?: StoreEnhancer<Ext, StateExt>
-): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext {
+): Store<S, A, StateExt> & Ext {
   return createStore(reducer, preloadedState as any, enhancer)
 }
diff --git a/src/types/store.ts b/src/types/store.ts
index 488092b2a2..fb5b1a1d5f 100644
--- a/src/types/store.ts
+++ b/src/types/store.ts
@@ -133,13 +133,11 @@ export type Observer<T> = {
  * @template S The type of state held by this store.
  * @template A the type of actions which may be dispatched by this store.
  * @template StateExt any extension to state from store enhancers
- * @template Ext any extensions to the store from store enhancers
  */
 export interface Store<
   S = any,
   A extends Action = AnyAction,
-  StateExt = never,
-  Ext = {}
+  StateExt = never
 > {
   /**
    * Dispatches an action. It is the only way to trigger a state change.
@@ -174,7 +172,7 @@ export interface Store<
    *
    * @returns The current state tree of your application.
    */
-  getState(): S
+  getState(): ExtendState<S, StateExt>
 
   /**
    * Adds a change listener. It will be called any time an action is
@@ -211,9 +209,7 @@ export interface Store<
    *
    * @param nextReducer The reducer for the store to use instead.
    */
-  replaceReducer<NewState, NewActions extends Action>(
-    nextReducer: Reducer<NewState, NewActions>
-  ): Store<ExtendState<NewState, StateExt>, NewActions, StateExt, Ext> & Ext
+  replaceReducer(nextReducer: Reducer<S, A>): void
 
   /**
    * Interoperability point for observable/reactive libraries.
@@ -221,7 +217,7 @@ export interface Store<
    * For more information, see the observable proposal:
    * https://github.com/tc39/proposal-observable
    */
-  [Symbol.observable](): Observable<S>
+  [Symbol.observable](): Observable<ExtendState<S, StateExt>>
 }
 
 /**
@@ -239,12 +235,12 @@ export interface StoreCreator {
   <S, A extends Action, Ext = {}, StateExt = never>(
     reducer: Reducer<S, A>,
     enhancer?: StoreEnhancer<Ext, StateExt>
-  ): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+  ): Store<S, A, StateExt> & Ext
   <S, A extends Action, Ext = {}, StateExt = never>(
     reducer: Reducer<S, A>,
     preloadedState?: PreloadedState<S>,
     enhancer?: StoreEnhancer<Ext>
-  ): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+  ): Store<S, A, StateExt> & Ext
 }
 
 /**
@@ -277,4 +273,4 @@ export type StoreEnhancerStoreCreator<Ext = {}, StateExt = never> = <
 >(
   reducer: Reducer<S, A>,
   preloadedState?: PreloadedState<S>
-) => Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+) => Store<S, A, StateExt> & Ext
diff --git a/test/combineReducers.spec.ts b/test/combineReducers.spec.ts
index eeff719eb1..898c3bc215 100644
--- a/test/combineReducers.spec.ts
+++ b/test/combineReducers.spec.ts
@@ -327,14 +327,16 @@ describe('Utils', () => {
       const ACTION = { type: 'ACTION' }
 
       it('should return an updated state when additional reducers are passed to combineReducers', function () {
-        const originalCompositeReducer = combineReducers({ foo })
+        type State = { foo: {}; bar?: {} }
+
+        const originalCompositeReducer = combineReducers<State>({ foo })
         const store = createStore(originalCompositeReducer)
 
         store.dispatch(ACTION)
 
         const initialState = store.getState()
 
-        store.replaceReducer(combineReducers({ foo, bar }))
+        store.replaceReducer(combineReducers<State>({ foo, bar }))
         store.dispatch(ACTION)
 
         const nextState = store.getState()
@@ -342,16 +344,18 @@ describe('Utils', () => {
       })
 
       it('should return an updated state when reducers passed to combineReducers are changed', function () {
+        type State = { foo?: {}; bar: {}; baz?: {} }
+
         const baz = (state = {}) => state
 
-        const originalCompositeReducer = combineReducers({ foo, bar })
+        const originalCompositeReducer = combineReducers<State>({ foo, bar })
         const store = createStore(originalCompositeReducer)
 
         store.dispatch(ACTION)
 
         const initialState = store.getState()
 
-        store.replaceReducer(combineReducers({ baz, bar }))
+        store.replaceReducer(combineReducers<State>({ baz, bar }))
         store.dispatch(ACTION)
 
         const nextState = store.getState()
@@ -374,7 +378,9 @@ describe('Utils', () => {
       })
 
       it('should return an updated state when one of more reducers passed to the combineReducers are removed', function () {
-        const originalCompositeReducer = combineReducers({ foo, bar })
+        const originalCompositeReducer = combineReducers<{ foo?: {}; bar: {} }>(
+          { foo, bar }
+        )
         const store = createStore(originalCompositeReducer)
 
         store.dispatch(ACTION)
diff --git a/test/createStore.spec.ts b/test/createStore.spec.ts
index f8065aeb61..3b82f37b2e 100644
--- a/test/createStore.spec.ts
+++ b/test/createStore.spec.ts
@@ -824,7 +824,7 @@ describe('createStore', () => {
     console.error = jest.fn()
 
     const store = createStore(
-      combineReducers({
+      combineReducers<{ x?: number; y: { z: number; w?: number } }>({
         x: (s = 0, _) => s,
         y: combineReducers({
           z: (s = 0, _) => s,
diff --git a/test/replaceReducers.spec.ts b/test/replaceReducers.spec.ts
deleted file mode 100644
index ed70106b12..0000000000
--- a/test/replaceReducers.spec.ts
+++ /dev/null
@@ -1,18 +0,0 @@
-import { createStore, combineReducers } from '..'
-
-describe('replaceReducers test', () => {
-  it('returns the original store', () => {
-    const nextReducer = combineReducers({
-      foo: (state = 1, _action) => state,
-      bar: (state = 2, _action) => state
-    })
-    const store = createStore((state, action) => {
-      if (state === undefined) return { type: 5 }
-      return action
-    })
-
-    const nextStore = store.replaceReducer(nextReducer)
-
-    expect(nextStore).toBe(store)
-  })
-})
diff --git a/test/typescript/enhancers.ts b/test/typescript/enhancers.ts
index 0ec1bdcfad..16cb9b3f3c 100644
--- a/test/typescript/enhancers.ts
+++ b/test/typescript/enhancers.ts
@@ -1,4 +1,11 @@
-import { StoreEnhancer, Action, AnyAction, Reducer, createStore } from '../..'
+import {
+  StoreEnhancer,
+  Action,
+  AnyAction,
+  Reducer,
+  createStore,
+  Store
+} from '../..'
 
 interface State {
   someField: 'string'
@@ -131,22 +138,27 @@ function replaceReducerExtender() {
       return createStore(wrappedReducer, wrappedPreloadedState)
     }
 
-  const store = createStore(reducer, enhancer)
+  const store = createStore<
+    { someField?: 'string'; test?: boolean },
+    Action<unknown>,
+    { method(): string },
+    ExtraState
+  >(reducer, enhancer)
 
   const newReducer = (
     state: { test: boolean } = { test: true },
     _: AnyAction
   ) => state
 
-  const newStore = store.replaceReducer(newReducer)
-  newStore.getState().test
-  newStore.getState().extraField
+  store.replaceReducer(newReducer)
+  store.getState().test
+  store.getState().extraField
   // @ts-expect-error
-  newStore.getState().wrongField
+  store.getState().wrongField
 
-  const res: string = newStore.method()
+  const res: string = store.method()
   // @ts-expect-error
-  newStore.wrongMethod()
+  store.wrongMethod()
 }
 
 function mhelmersonExample() {
@@ -187,13 +199,8 @@ function mhelmersonExample() {
         const store = createStore(wrappedReducer, wrappedPreloadedState)
         return {
           ...store,
-          replaceReducer<NS, NA extends Action = AnyAction>(
-            nextReducer: (
-              state: (NS & ExtraState) | undefined,
-              action: NA
-            ) => NS & ExtraState
-          ) {
-            const nextWrappedReducer: Reducer<NS & ExtraState, NA> = (
+          replaceReducer(nextReducer: Reducer<S, A>) {
+            const nextWrappedReducer: Reducer<S & ExtraState, A> = (
               state,
               action
             ) => {
@@ -208,13 +215,17 @@ function mhelmersonExample() {
         }
       }
 
-    const store = createStore(reducer, enhancer)
+    const store = createStore<
+      { someField?: 'string'; test?: boolean },
+      Action<unknown>,
+      {},
+      ExtraState
+    >(reducer, enhancer)
     store.replaceReducer(reducer)
 
     store.getState().extraField
     // @ts-expect-error
     store.getState().wrongField
-    // @ts-expect-error
     store.getState().test
 
     const newReducer = (
@@ -222,11 +233,11 @@ function mhelmersonExample() {
       _: AnyAction
     ) => state
 
-    const newStore = store.replaceReducer(newReducer)
-    newStore.getState().test
-    newStore.getState().extraField
+    store.replaceReducer(newReducer)
+    store.getState().test
+    store.getState().extraField
     // @ts-expect-error
-    newStore.getState().wrongField
+    store.getState().wrongField
   }
 }
 
@@ -235,12 +246,12 @@ function finalHelmersonExample() {
     foo: string
   }
 
-  function persistReducer<S, A extends AnyAction>(
+  function persistReducer<S, A extends Action<unknown>>(
     config: any,
     reducer: Reducer<S, A>
   ) {
-    return (state: (S & ExtraState) | undefined, action: AnyAction) => {
-      const newState = reducer(state, action as unknown as A)
+    return (state: (S & ExtraState) | undefined, action: A) => {
+      const newState = reducer(state, action)
       return {
         ...newState,
         foo: 'hi'
@@ -256,10 +267,10 @@ function finalHelmersonExample() {
     persistConfig: any
   ): StoreEnhancer<{}, ExtraState> {
     return createStore =>
-      <S, A extends Action = AnyAction>(
+      <S, A extends Action<unknown>>(
         reducer: Reducer<S, A>,
         preloadedState?: any
-      ) => {
+      ): Store<S, A, ExtraState> & { persistor: Store<S, A, ExtraState> } => {
         const persistedReducer = persistReducer<S, A>(persistConfig, reducer)
         const store = createStore(persistedReducer, preloadedState)
         const persistor = persistStore(store)
@@ -267,16 +278,19 @@ function finalHelmersonExample() {
         return {
           ...store,
           replaceReducer: nextReducer => {
-            return store.replaceReducer(
-              persistReducer(persistConfig, nextReducer)
-            )
+            store.replaceReducer(persistReducer(persistConfig, nextReducer))
           },
           persistor
         }
       }
   }
 
-  const store = createStore(reducer, createPersistEnhancer('hi'))
+  const store = createStore<
+    { someField?: 'string'; test?: boolean },
+    Action<unknown>,
+    {},
+    ExtraState
+  >(reducer, createPersistEnhancer('hi'))
 
   store.getState().foo
   // @ts-expect-error
@@ -287,10 +301,10 @@ function finalHelmersonExample() {
     _: AnyAction
   ) => state
 
-  const newStore = store.replaceReducer(newReducer)
-  newStore.getState().test
+  store.replaceReducer(newReducer)
+  store.getState().test
   // @ts-expect-error
-  newStore.getState().whatever
+  store.getState().whatever
   // @ts-expect-error
-  newStore.getState().wrongField
+  store.getState().wrongField
 }
diff --git a/test/typescript/replaceReducer.ts b/test/typescript/replaceReducer.ts
deleted file mode 100644
index 66d6bca156..0000000000
--- a/test/typescript/replaceReducer.ts
+++ /dev/null
@@ -1,26 +0,0 @@
-import { combineReducers, createStore } from '../..'
-
-/**
- * verify that replaceReducer maintains strict typing if the new types change
- */
-const bar = (state = { value: 'bar' }) => state
-const baz = (state = { value: 'baz' }) => state
-const ACTION = {
-  type: 'action'
-}
-
-const originalCompositeReducer = combineReducers({ bar })
-const store = createStore(originalCompositeReducer)
-store.dispatch(ACTION)
-
-const firstState = store.getState()
-firstState.bar.value
-// @ts-expect-error
-firstState.baz.value
-
-const nextStore = store.replaceReducer(combineReducers({ baz })) // returns ->  { baz: { value: 'baz' }}
-
-const nextState = nextStore.getState()
-// @ts-expect-error
-nextState.bar.value
-nextState.baz.value