diff --git a/lib/components/term.tsx b/lib/components/term.tsx
index 844836bc..5e48570f 100644
--- a/lib/components/term.tsx
+++ b/lib/components/term.tsx
@@ -11,7 +11,6 @@ import Color from 'color';
 import terms from '../terms';
 import processClipboard from '../utils/paste';
 import SearchBox from './searchBox';
-import ResizeObserver from 'resize-observer-polyfill';
 import {TermProps} from '../hyper';
 import {ObjectTypedKeys} from '../utils/object';
 
diff --git a/lib/hyper.d.ts b/lib/hyper.d.ts
index d503354e..ed33bbe5 100644
--- a/lib/hyper.d.ts
+++ b/lib/hyper.d.ts
@@ -162,8 +162,11 @@ export type hyperPlugin = {
   reduceUI: IUiReducer;
 };
 
-import rootReducer from './reducers/index';
-export type HyperState = ReturnType<typeof rootReducer>;
+export type HyperState = {
+  ui: Immutable<uiState>;
+  sessions: Immutable<sessionState>;
+  termGroups: Immutable<ITermState>;
+};
 
 import {UIActions} from './constants/ui';
 import {ConfigActions} from './constants/config';
diff --git a/lib/reducers/index.ts b/lib/reducers/index.ts
index 74228dac..95de7d3b 100644
--- a/lib/reducers/index.ts
+++ b/lib/reducers/index.ts
@@ -1,18 +1,11 @@
-import {combineReducers} from 'redux';
-import ui, {IUiReducer} from './ui';
-import sessions, {ISessionReducer} from './sessions';
-import termGroups, {ITermGroupReducer} from './term-groups';
-import {HyperActions} from '../hyper';
+import {combineReducers, Reducer} from 'redux';
+import ui from './ui';
+import sessions from './sessions';
+import termGroups from './term-groups';
+import {HyperActions, HyperState} from '../hyper';
 
-export default combineReducers<
-  {
-    ui: ReturnType<IUiReducer>;
-    sessions: ReturnType<ISessionReducer>;
-    termGroups: ReturnType<ITermGroupReducer>;
-  },
-  HyperActions
->({
+export default combineReducers({
   ui,
   sessions,
   termGroups
-});
+}) as Reducer<HyperState, HyperActions>;
diff --git a/package.json b/package.json
index 444992ec..415e11eb 100644
--- a/package.json
+++ b/package.json
@@ -116,7 +116,6 @@
     "prettier": "2.2.1",
     "proxyquire": "2.1.3",
     "redux-devtools-extension": "2.13.8",
-    "resize-observer-polyfill": "1.5.1",
     "spectron": "13.0.0",
     "style-loader": "2.0.0",
     "terser": "5.6.0",
diff --git a/yarn.lock b/yarn.lock
index 0102787e..924595c6 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -6480,11 +6480,6 @@ reselect@4.0.0:
   resolved "https://registry.npmjs.org/reselect/-/reselect-4.0.0.tgz#f2529830e5d3d0e021408b246a206ef4ea4437f7"
   integrity sha512-qUgANli03jjAyGlnbYVAV5vvnOmJnODyABz51RdBN7M4WaVu8mecZWgyQNkG8Yqe3KRGRt0l4K4B3XVEULC4CA==
 
-resize-observer-polyfill@1.5.1:
-  version "1.5.1"
-  resolved "https://registry.npmjs.org/resize-observer-polyfill/-/resize-observer-polyfill-1.5.1.tgz#0e9020dd3d21024458d4ebd27e23e40269810464"
-  integrity sha512-LwZrotdHOo12nQuZlHEmtuXdqGoOD0OhaxopaNFxWzInpEgaLWoVuAMbTzixuosCx2nEG58ngzW3vxdWoxIgdg==
-
 resolve-alpn@^1.0.0:
   version "1.0.0"
   resolved "https://registry.npmjs.org/resolve-alpn/-/resolve-alpn-1.0.0.tgz#745ad60b3d6aff4b4a48e01b8c0bdc70959e0e8c"