diff --git a/packages/node_modules/overmind/src/statemachine.test.ts b/packages/node_modules/overmind/src/statemachine.test.ts
index de9f40e3..4b8e1623 100644
--- a/packages/node_modules/overmind/src/statemachine.test.ts
+++ b/packages/node_modules/overmind/src/statemachine.test.ts
@@ -456,25 +456,40 @@ describe('Statemachine', () => {
 
     expect(() => overmind.actions.transition()).not.toThrow()
   })
-  test('should deal with transition effects', async () => {
+  test('should dispose nested machines', async () => {
     type States = {
       current: 'FOO'
     } | {
       current: 'BAR',
-      number: number
     }
 
-    const state = statemachine<States>({
+    type ParentStates = {
+      current: 'FOO'
+      nested: typeof nested 
+    } | {
+      current: 'BAR'
+    }
+
+    const nested = statemachine<States>({
+      FOO: ['BAR'],
+      BAR: ['FOO']
+    }, {
+      current: 'FOO'
+    })
+
+    const state = statemachine<ParentStates>({
       FOO: ['BAR'],
       BAR: ['FOO']
     }, {
       current: 'FOO',
+      nested 
     })
     const transition: Action = ({ state }) => {
-      return state.transition('BAR', { number: 123 }, () => {
-        return Promise.resolve(4321)
-      }, (barState, value) => {
-          barState.number = value
+      state.matches('FOO', (fooState) => {
+        const ref = fooState.nested
+        state.transition('BAR', {})
+        expect(fooState.nested).toBe(undefined)
+        expect(ref.current).toBe('FOO')
       })
     }
 
@@ -485,13 +500,12 @@ describe('Statemachine', () => {
       }
     } 
 
-    interface Action extends IAction<typeof config, void, Promise<void>> {}
+    interface Action extends IAction<typeof config, void, void> {}
 
     const overmind = createOvermindMock(config)
     // @ts-ignore
     overmind.isStrict = true
     
-    await overmind.actions.transition()
-    expect(overmind.state.current === 'BAR' && overmind.state.number === 4321).toBe(true)
+    overmind.actions.transition()
   })
 })
diff --git a/packages/node_modules/overmind/src/statemachine.ts b/packages/node_modules/overmind/src/statemachine.ts
index 918837e2..f5d1fc5f 100644
--- a/packages/node_modules/overmind/src/statemachine.ts
+++ b/packages/node_modules/overmind/src/statemachine.ts
@@ -1,4 +1,4 @@
-import { PROXY_TREE, VALUE } from 'proxy-state-tree'
+import { PROXY_TREE, VALUE, PATH } from 'proxy-state-tree'
 
 import { deepCopy } from './utils'
 import { IState } from '.'
@@ -34,18 +34,15 @@ export interface MachineMethods<States extends TStates, Base extends IState = {}
   matches<T extends States["current"], O = void>(state: T | T[], cb: (current: Statemachine<Base, States, States extends {
     current: T
   } ? States : never>) => O): O;
-  transition<T extends States["current"], O = void, O2 = O>(
+  transition<T extends States["current"], O = void>(
     state: T,
     newState: States extends {
       current: T  
     } ? Exact<Omit<States, 'current'>, {}> extends never ?  Omit<States, 'current'> & Partial<Base> : Exact<Partial<Base>, {}> extends never ? Partial<Base> : { [NO_PROP]?: true} : never,
     effectsCallback?: ((current: Statemachine<Base, States, States extends {
       current: T
-    } ? States : never>) => O),
-    stateCallback?: ((current: Statemachine<Base, States, States extends {
-      current: T
-    } ? States : never>, value: O extends Promise<infer V> ? V : O) => O2)
-  ): O extends Promise<any> ? Promise<O2> : O2;
+    } ? States : never>) => O)
+  ): O;
 }
 
 export type Statemachine<Base extends IState, States extends TStates, State extends TStates = States> = Base extends never ? State & MachineMethods<States> : Base & State & MachineMethods<States, Base>
@@ -56,15 +53,20 @@ const BASE = Symbol('BASE')
 const STATE = Symbol('STATE')
 const CURRENT_KEYS = Symbol('CURRENT_KEYS')
 const NO_PROP = Symbol('NO_PROP')
+const IS_DISPOSED = Symbol('IS_DISPOSED')
 
 export class StateMachine<Base extends IState, States extends TStates, State extends TStates = States, >  {
   current: State["current"]
   private [INITIAL_STATE]: State["current"]
   private [STATE]: any
   private [BASE]: any
+  private [IS_DISPOSED] = false
   private clone() {
     return new StateMachine(this[TRANSITIONS], deepCopy(this[STATE]), deepCopy(this[BASE]))
   }
+  private dispose() {
+    this
+  }
   constructor(transitions: StatemachineTransitions<States>, state: States, base: Base) {
     this[STATE] = state
     this[INITIAL_STATE] = state.current
@@ -74,6 +76,13 @@ export class StateMachine<Base extends IState, States extends TStates, State ext
     Object.assign(this, state, base)
   }
   matches(states, cb) {
+    if (this[VALUE][IS_DISPOSED]) {
+      if (process.env.NODE_ENV === 'development') {
+        console.warn(`Overmind - The statemachine at "${this[PATH]}" has been disposed, but you tried to match on it`)
+      }
+      return
+    }
+
     states = Array.isArray(states) ? states : [states]
 
     if (states.includes(this.current)) {
@@ -89,7 +98,14 @@ export class StateMachine<Base extends IState, States extends TStates, State ext
       return result
     }
   }
-  transition(state, newState, effectsCallback, stateCallback) {
+  transition(state, newState, effectsCallback) {
+    if (this[VALUE][IS_DISPOSED]) {
+      if (process.env.NODE_ENV === 'development') {
+        console.warn(`Overmind - The statemachine at "${this[PATH]}" has been disposed, but you tried to transition on it`)
+      }
+      return
+    }
+
     const transitions = this[VALUE][TRANSITIONS] 
 
     if (transitions[this.current].includes(state)) {
@@ -100,6 +116,9 @@ export class StateMachine<Base extends IState, States extends TStates, State ext
 
       this[VALUE][CURRENT_KEYS].forEach((key) => {
         if (!baseKeys.includes(key)) {
+          if (this[key] instanceof StateMachine) {
+            this[key].dispose()
+          }
           delete this[key]
         }
       })
@@ -115,18 +134,6 @@ export class StateMachine<Base extends IState, States extends TStates, State ext
         result = effectsCallback(this)
       }
 
-      if (stateCallback && result instanceof Promise) {
-        return result.then((value) => {
-          if (this.current !== state) {
-            return value
-          }
-          tree.enableMutations()
-          const result = stateCallback(this, value)
-          tree.blockMutations()
-          return result
-        })
-      }
-
       return result
     } else if (process.env.NODE_ENV === 'development' && state !== this.current) {
       console.warn(`Overmind Statemachine - You tried to transition into "${state}", but it is not a valid transition. The valid transitions are ${JSON.stringify(transitions[this.current])}`)