diff --git a/lib/keyserver-conn/keyserver-conn-types.js b/lib/keyserver-conn/keyserver-conn-types.js
--- a/lib/keyserver-conn/keyserver-conn-types.js
+++ b/lib/keyserver-conn/keyserver-conn-types.js
@@ -18,9 +18,9 @@
   SUCCESS_ACTION_TYPE: string,
   FAILED_ACTION_TYPE: string,
 > = {
-  started: STARTED_ACTION_TYPE,
-  success: SUCCESS_ACTION_TYPE,
-  failed: FAILED_ACTION_TYPE,
+  +started: STARTED_ACTION_TYPE,
+  +success: SUCCESS_ACTION_TYPE,
+  +failed: FAILED_ACTION_TYPE,
 };
 
 export const setNewSessionActionType = 'SET_NEW_SESSION';
diff --git a/lib/media/file-utils.js b/lib/media/file-utils.js
--- a/lib/media/file-utils.js
+++ b/lib/media/file-utils.js
@@ -18,7 +18,7 @@
     +loop: boolean,
   }>,
 };
-const mediaConfig: { [mime: string]: MediaConfig } = Object.freeze({
+const mediaConfig: { +[mime: string]: MediaConfig } = Object.freeze({
   'image/png': {
     mediaType: 'photo',
     extension: 'png',
diff --git a/lib/shared/messages/message-specs.js b/lib/shared/messages/message-specs.js
--- a/lib/shared/messages/message-specs.js
+++ b/lib/shared/messages/message-specs.js
@@ -29,7 +29,7 @@
 } from '../../types/message-types-enum.js';
 
 export const messageSpecs: {
-  [MessageType]: MessageSpec<*, *, *>,
+  +[MessageType]: MessageSpec<*, *, *>,
 } = Object.freeze({
   [messageTypes.TEXT]: textMessageSpec,
   [messageTypes.CREATE_THREAD]: createThreadMessageSpec,