diff --git a/lib/flow-typed/npm/redux_v4.x.x.js b/lib/flow-typed/npm/redux_v4.x.x.js
--- a/lib/flow-typed/npm/redux_v4.x.x.js
+++ b/lib/flow-typed/npm/redux_v4.x.x.js
@@ -14,7 +14,7 @@
 
   declare export type DispatchAPI<A> = (action: A) => A;
 
-  declare export type Dispatch<A: { type: any, ... }> = DispatchAPI<A>;
+  declare export type Dispatch<A: $ReadOnly<{ type: any, ... }>> = DispatchAPI<A>;
 
   declare export type MiddlewareAPI<S, A, D = Dispatch<A>> = {
     dispatch: D,
diff --git a/web/flow-typed/npm/redux_v4.x.x.js b/web/flow-typed/npm/redux_v4.x.x.js
--- a/web/flow-typed/npm/redux_v4.x.x.js
+++ b/web/flow-typed/npm/redux_v4.x.x.js
@@ -14,7 +14,7 @@
 
   declare export type DispatchAPI<A> = (action: A) => A;
 
-  declare export type Dispatch<A: { type: any, ... }> = DispatchAPI<A>;
+  declare export type Dispatch<A: $ReadOnly<{ type: any, ... }>> = DispatchAPI<A>;
 
   declare export type MiddlewareAPI<S, A, D = Dispatch<A>> = {
     dispatch: D,
diff --git a/web/redux/tab-synchronization.js b/web/redux/tab-synchronization.js
--- a/web/redux/tab-synchronization.js
+++ b/web/redux/tab-synchronization.js
@@ -1,13 +1,13 @@
 // @flow
 
-import type { Middleware, Store } from 'redux';
+import type { Middleware, Store, Dispatch } from 'redux';
 
 import type { Action, AppState } from './redux-setup.js';
 
 const WEB_REDUX_CHANNEL = new BroadcastChannel('shared-redux');
 
 const tabSynchronizationMiddleware: Middleware<AppState, Action> =
-  () => next => action => {
+  () => (next: Dispatch<Action>) => (action: Action) => {
     const result = next(action);
     // For now the `dispatchSource` field is not included in any of the
     // redux actions and this causes flow to throw an error.