diff --git a/packages/react-debug-tools/src/ReactDebugHooks.js b/packages/react-debug-tools/src/ReactDebugHooks.js
index b53fab87d46d8..cd25588220fe5 100644
--- a/packages/react-debug-tools/src/ReactDebugHooks.js
+++ b/packages/react-debug-tools/src/ReactDebugHooks.js
@@ -142,7 +142,7 @@ function useRef<T>(initialValue: T): {current: T} {
 }
 
 function useLayoutEffect(
-  create: () => mixed,
+  create: () => (() => void) | void,
   inputs: Array<mixed> | void | null,
 ): void {
   nextHook();
@@ -154,7 +154,7 @@ function useLayoutEffect(
 }
 
 function useEffect(
-  create: () => mixed,
+  create: () => (() => void) | void,
   inputs: Array<mixed> | void | null,
 ): void {
   nextHook();
diff --git a/packages/react-dom/src/server/ReactPartialRendererHooks.js b/packages/react-dom/src/server/ReactPartialRendererHooks.js
index 558c34064b2c5..134f9e1a80b45 100644
--- a/packages/react-dom/src/server/ReactPartialRendererHooks.js
+++ b/packages/react-dom/src/server/ReactPartialRendererHooks.js
@@ -329,7 +329,7 @@ function useRef<T>(initialValue: T): {current: T} {
 }
 
 export function useLayoutEffect(
-  create: () => mixed,
+  create: () => (() => void) | void,
   inputs: Array<mixed> | void | null,
 ) {
   if (__DEV__) {
diff --git a/packages/react-reconciler/src/ReactFiberHooks.js b/packages/react-reconciler/src/ReactFiberHooks.js
index a75f5cb212921..646cbc4464457 100644
--- a/packages/react-reconciler/src/ReactFiberHooks.js
+++ b/packages/react-reconciler/src/ReactFiberHooks.js
@@ -66,8 +66,8 @@ export type Hook = {
 
 type Effect = {
   tag: HookEffectTag,
-  create: () => mixed,
-  destroy: (() => mixed) | null,
+  create: () => (() => void) | void,
+  destroy: (() => void) | null,
   deps: Array<mixed> | null,
   next: Effect,
 };
@@ -608,7 +608,7 @@ export function useRef<T>(initialValue: T): {current: T} {
 }
 
 export function useLayoutEffect(
-  create: () => mixed,
+  create: () => (() => void) | void,
   deps: Array<mixed> | void | null,
 ): void {
   if (__DEV__) {
@@ -618,7 +618,7 @@ export function useLayoutEffect(
 }
 
 export function useEffect(
-  create: () => mixed,
+  create: () => (() => void) | void,
   deps: Array<mixed> | void | null,
 ): void {
   if (__DEV__) {
@@ -679,7 +679,9 @@ export function useImperativeHandle<T>(
       const refCallback = ref;
       const inst = create();
       refCallback(inst);
-      return () => refCallback(null);
+      return () => {
+        refCallback(null);
+      };
     } else if (ref !== null && ref !== undefined) {
       const refObject = ref;
       const inst = create();
diff --git a/packages/react/src/ReactHooks.js b/packages/react/src/ReactHooks.js
index 37f85cd5c3537..dc35ed8c5e780 100644
--- a/packages/react/src/ReactHooks.js
+++ b/packages/react/src/ReactHooks.js
@@ -71,7 +71,7 @@ export function useRef<T>(initialValue: T): {current: T} {
 }
 
 export function useEffect(
-  create: () => mixed,
+  create: () => (() => void) | void,
   inputs: Array<mixed> | void | null,
 ) {
   const dispatcher = resolveDispatcher();
@@ -79,7 +79,7 @@ export function useEffect(
 }
 
 export function useLayoutEffect(
-  create: () => mixed,
+  create: () => (() => void) | void,
   inputs: Array<mixed> | void | null,
 ) {
   const dispatcher = resolveDispatcher();