diff --git a/packages/core/src/getStateFromPath.tsx b/packages/core/src/getStateFromPath.tsx
index e1e57831..c3d6cf51 100644
--- a/packages/core/src/getStateFromPath.tsx
+++ b/packages/core/src/getStateFromPath.tsx
@@ -260,6 +260,7 @@ export default function getStateFromPath(
   );
 
   if (params) {
+    // @ts-expect-error: params should be treated as read-only, but we're creating the state here so it doesn't matter
     route.params = { ...route.params, ...params };
   }
 
diff --git a/packages/core/src/types.tsx b/packages/core/src/types.tsx
index c8f39682..dac13087 100644
--- a/packages/core/src/types.tsx
+++ b/packages/core/src/types.tsx
@@ -62,7 +62,9 @@ export type EventArg<
       preventDefault(): void;
     }
   : {}) &
-  (undefined extends Data ? { readonly data?: Data } : { readonly data: Data });
+  (undefined extends Data
+    ? { readonly data?: Readonly<Data> }
+    : { readonly data: Readonly<Data> });
 
 export type EventListenerCallback<
   EventMap extends EventMapBase,
@@ -277,18 +279,18 @@ export type RouteProp<
   RouteName extends keyof ParamList
 > = Omit<Route<Extract<RouteName, string>>, 'params'> &
   (undefined extends ParamList[RouteName]
-    ? {
+    ? Readonly<{
         /**
          * Params for this route
          */
-        params?: ParamList[RouteName];
-      }
-    : {
+        params?: Readonly<ParamList[RouteName]>;
+      }>
+    : Readonly<{
         /**
          * Params for this route
          */
-        params: ParamList[RouteName];
-      });
+        params: Readonly<ParamList[RouteName]>;
+      }>);
 
 export type CompositeNavigationProp<
   A extends NavigationProp<ParamListBase, string, any, any>,
diff --git a/packages/routers/src/types.tsx b/packages/routers/src/types.tsx
index 390aa641..81312da3 100644
--- a/packages/routers/src/types.tsx
+++ b/packages/routers/src/types.tsx
@@ -2,7 +2,7 @@ import type * as CommonActions from './CommonActions';
 
 export type CommonNavigationAction = CommonActions.Action;
 
-export type NavigationState = {
+export type NavigationState = Readonly<{
   /**
    * Unique key for the navigation state.
    */
@@ -35,26 +35,27 @@ export type NavigationState = {
    * Whether the navigation state has been rehydrated.
    */
   stale: false;
-};
+}>;
 
-export type InitialState = Partial<
-  Omit<NavigationState, 'stale' | 'routes'>
-> & {
-  routes: (Omit<Route<string>, 'key'> & { state?: InitialState })[];
-};
+export type InitialState = Readonly<
+  Partial<Omit<NavigationState, 'stale' | 'routes'>> & {
+    routes: (Omit<Route<string>, 'key'> & { state?: InitialState })[];
+  }
+>;
 
 export type PartialState<State extends NavigationState> = Partial<
   Omit<State, 'stale' | 'type' | 'key' | 'routes' | 'routeNames'>
-> & {
-  stale?: true;
-  type?: string;
-  routes: (Omit<Route<string>, 'key'> & {
-    key?: string;
-    state?: InitialState;
-  })[];
-};
+> &
+  Readonly<{
+    stale?: true;
+    type?: string;
+    routes: (Omit<Route<string>, 'key'> & {
+      key?: string;
+      state?: InitialState;
+    })[];
+  }>;
 
-export type Route<RouteName extends string> = {
+export type Route<RouteName extends string> = Readonly<{
   /**
    * Unique key for the route.
    */
@@ -67,11 +68,11 @@ export type Route<RouteName extends string> = {
    * Params for the route.
    */
   params?: object;
-};
+}>;
 
 export type ParamListBase = Record<string, object | undefined>;
 
-export type NavigationAction = {
+export type NavigationAction = Readonly<{
   /**
    * Type of the action (e.g. `NAVIGATE`)
    */
@@ -88,7 +89,7 @@ export type NavigationAction = {
    * Key of the navigator which should handle this action.
    */
   target?: string;
-};
+}>;
 
 export type ActionCreators<Action extends NavigationAction> = {
   [key: string]: (...args: any) => Action;