diff --git a/native/calendar/loading-indicator.react.js b/native/calendar/loading-indicator.react.js
--- a/native/calendar/loading-indicator.react.js
+++ b/native/calendar/loading-indicator.react.js
@@ -7,9 +7,9 @@
 import type { LoadingStatus } from 'lib/types/loading-types';
 
 type Props = {
-  loadingStatus: LoadingStatus,
-  color: string,
-  canUseRed: boolean,
+  +loadingStatus: LoadingStatus,
+  +color: string,
+  +canUseRed: boolean,
 };
 function LoadingIndicator(props: Props): React.Node {
   if (props.loadingStatus === 'error') {
diff --git a/native/calendar/thread-picker-modal.react.js b/native/calendar/thread-picker-modal.react.js
--- a/native/calendar/thread-picker-modal.react.js
+++ b/native/calendar/thread-picker-modal.react.js
@@ -26,8 +26,8 @@
 };
 
 type Props = {
-  navigation: RootNavigationProp<'ThreadPickerModal'>,
-  route: NavigationRoute<'ThreadPickerModal'>,
+  +navigation: RootNavigationProp<'ThreadPickerModal'>,
+  +route: NavigationRoute<'ThreadPickerModal'>,
 };
 function ThreadPickerModal(props: Props): React.Node {
   const {
diff --git a/native/chat/new-messages-pill.react.js b/native/chat/new-messages-pill.react.js
--- a/native/chat/new-messages-pill.react.js
+++ b/native/chat/new-messages-pill.react.js
@@ -8,10 +8,10 @@
 import type { ViewStyle } from '../types/styles';
 
 type Props = {
-  onPress: () => mixed,
-  newMessageCount: number,
-  containerStyle?: ViewStyle,
-  style?: ViewStyle,
+  +onPress: () => mixed,
+  +newMessageCount: number,
+  +containerStyle?: ViewStyle,
+  +style?: ViewStyle,
   ...React.ElementConfig<typeof View>,
 };
 function NewMessagesPill(props: Props): React.Node {
diff --git a/native/components/clearable-text-input.react.ios.js b/native/components/clearable-text-input.react.ios.js
--- a/native/components/clearable-text-input.react.ios.js
+++ b/native/components/clearable-text-input.react.ios.js
@@ -9,7 +9,7 @@
 import TextInput from './text-input.react';
 
 type State = {
-  textInputKey: number,
+  +textInputKey: number,
 };
 class ClearableTextInput extends React.PureComponent<
   ClearableTextInputProps,
diff --git a/native/components/content-loading.react.js b/native/components/content-loading.react.js
--- a/native/components/content-loading.react.js
+++ b/native/components/content-loading.react.js
@@ -6,8 +6,8 @@
 import type { Colors } from '../themes/colors';
 
 type Props = {
-  fillType: 'flex' | 'absolute',
-  colors: Colors,
+  +fillType: 'flex' | 'absolute',
+  +colors: Colors,
 };
 function ContentLoading(props: Props): React.Node {
   const viewStyle =
diff --git a/native/components/single-line.react.js b/native/components/single-line.react.js
--- a/native/components/single-line.react.js
+++ b/native/components/single-line.react.js
@@ -7,7 +7,7 @@
 
 type Props = {
   ...React.ElementConfig<typeof Text>,
-  children: ?string,
+  +children: ?string,
 };
 function SingleLine(props: Props): React.Node {
   const text = firstLine(props.children);
diff --git a/native/error-boundary.react.js b/native/error-boundary.react.js
--- a/native/error-boundary.react.js
+++ b/native/error-boundary.react.js
@@ -16,10 +16,10 @@
 });
 
 type Props = {
-  children: React.Node,
+  +children: React.Node,
 };
 type State = {
-  errorData: $ReadOnlyArray<ErrorData>,
+  +errorData: $ReadOnlyArray<ErrorData>,
 };
 class ErrorBoundary extends React.PureComponent<Props, State> {
   state: State = {
diff --git a/native/media/send-media-button.react.js b/native/media/send-media-button.react.js
--- a/native/media/send-media-button.react.js
+++ b/native/media/send-media-button.react.js
@@ -15,10 +15,10 @@
 
 type Props = {
   ...React.ElementConfig<typeof View>,
-  onPress: () => mixed,
-  queueCount?: number,
-  containerStyle?: ViewStyle,
-  style?: ViewStyle,
+  +onPress: () => mixed,
+  +queueCount?: number,
+  +containerStyle?: ViewStyle,
+  +style?: ViewStyle,
 };
 function SendMediaButton(props: Props): React.Node {
   const {
diff --git a/native/navigation/action-result-modal.react.js b/native/navigation/action-result-modal.react.js
--- a/native/navigation/action-result-modal.react.js
+++ b/native/navigation/action-result-modal.react.js
@@ -17,8 +17,8 @@
 };
 
 type Props = {
-  navigation: AppNavigationProp<'ActionResultModal'>,
-  route: NavigationRoute<'ActionResultModal'>,
+  +navigation: AppNavigationProp<'ActionResultModal'>,
+  +route: NavigationRoute<'ActionResultModal'>,
 };
 function ActionResultModal(props: Props): React.Node {
   const overlayContext = React.useContext(OverlayContext);
diff --git a/native/navigation/header.react.js b/native/navigation/header.react.js
--- a/native/navigation/header.react.js
+++ b/native/navigation/header.react.js
@@ -7,7 +7,7 @@
 
 type Props = {
   ...StackHeaderProps,
-  activeTab: boolean,
+  +activeTab: boolean,
 };
 export default function CustomHeader(props: Props): React.Node {
   const { activeTab, ...rest } = props;
diff --git a/native/navigation/modal-pruner.react.js b/native/navigation/modal-pruner.react.js
--- a/native/navigation/modal-pruner.react.js
+++ b/native/navigation/modal-pruner.react.js
@@ -92,7 +92,7 @@
 }
 
 type Props = {
-  navContext: NavContextType,
+  +navContext: NavContextType,
 };
 function ModalPruner(props: Props): null {
   const { state, dispatch } = props.navContext;
diff --git a/native/profile/custom-server-modal.react.js b/native/profile/custom-server-modal.react.js
--- a/native/profile/custom-server-modal.react.js
+++ b/native/profile/custom-server-modal.react.js
@@ -32,7 +32,7 @@
   +dispatch: Dispatch,
 };
 type State = {
-  customServer: string,
+  +customServer: string,
 };
 class CustomServerModal extends React.PureComponent<Props, State> {
   constructor(props: Props) {
diff --git a/native/push/in-app-notif.react.js b/native/push/in-app-notif.react.js
--- a/native/push/in-app-notif.react.js
+++ b/native/push/in-app-notif.react.js
@@ -10,9 +10,9 @@
 const edges = ['top'];
 
 type Props = {
-  title: ?string,
-  message: string,
-  activeTheme: ?GlobalTheme,
+  +title: ?string,
+  +message: string,
+  +activeTheme: ?GlobalTheme,
 };
 function InAppNotif(props: Props): React.Node {
   const useLightStyle = Platform.OS === 'ios' && props.activeTheme !== 'dark';
diff --git a/web/calendar/calendar.react.js b/web/calendar/calendar.react.js
--- a/web/calendar/calendar.react.js
+++ b/web/calendar/calendar.react.js
@@ -61,7 +61,7 @@
   ) => Promise<CalendarQueryUpdateResult>,
 };
 type State = {
-  filterPanelOpen: boolean,
+  +filterPanelOpen: boolean,
 };
 class Calendar extends React.PureComponent<Props, State> {
   state: State = {
diff --git a/web/chat/chat-message-list.react.js b/web/chat/chat-message-list.react.js
--- a/web/chat/chat-message-list.react.js
+++ b/web/chat/chat-message-list.react.js
@@ -69,8 +69,8 @@
   +inputState: ?InputState,
 };
 type ReactDnDProps = {
-  isActive: boolean,
-  connectDropTarget: (node: React.Node) => React.Node,
+  +isActive: boolean,
+  +connectDropTarget: (node: React.Node) => React.Node,
 };
 type Props = {
   ...PassedProps,