diff --git a/lib/permissions/dm-permissions.js b/lib/permissions/dm-permissions.js
--- a/lib/permissions/dm-permissions.js
+++ b/lib/permissions/dm-permissions.js
@@ -1,7 +1,5 @@
 // @flow
 
-import invariant from 'invariant';
-
 import { OPEN_CHILD, OPEN_DESCENDANT } from './prefixes.js';
 import {
   type ThreadRolePermissionsBlob,
@@ -9,14 +7,12 @@
 } from '../types/thread-permission-types.js';
 import {
   type ThickThreadType,
-  threadTypeIsThick,
   threadTypes,
 } from '../types/thread-types-enum.js';
 
 function getThickThreadRolePermissionsBlob(
   threadType: ThickThreadType,
 ): ThreadRolePermissionsBlob {
-  invariant(threadTypeIsThick(threadType), 'ThreadType should be thick');
   const openDescendantKnowOf = OPEN_DESCENDANT + threadPermissions.KNOW_OF;
   const openDescendantVisible = OPEN_DESCENDANT + threadPermissions.VISIBLE;
   const openChildJoinThread = OPEN_CHILD + threadPermissions.JOIN_THREAD;
diff --git a/lib/types/thread-types-enum.js b/lib/types/thread-types-enum.js
--- a/lib/types/thread-types-enum.js
+++ b/lib/types/thread-types-enum.js
@@ -75,11 +75,6 @@
   ...thickThreadTypes,
 });
 
-const thickThreadTypesSet = new Set(Object.values(thickThreadTypes));
-export function threadTypeIsThick(threadType: ThreadType): boolean {
-  return thickThreadTypesSet.has(threadType);
-}
-
 export function assertThinThreadType(threadType: number): ThinThreadType {
   invariant(
     threadType === 3 ||