diff --git a/lib/shared/mention-utils.js b/lib/shared/mention-utils.js
--- a/lib/shared/mention-utils.js
+++ b/lib/shared/mention-utils.js
@@ -1,7 +1,7 @@
 // @flow
 
 import { oldValidUsernameRegexString } from './account-utils.js';
-import SearchIndex from './search-index.js';
+import SentencePrefixSearchIndex from './sentence-prefix-search-index.js';
 import {
   threadOtherMembers,
   validChatNameRegexString,
@@ -65,7 +65,7 @@
 }
 
 function getMentionTypeaheadUserSuggestions(
-  userSearchIndex: SearchIndex,
+  userSearchIndex: SentencePrefixSearchIndex,
   threadMembers: $ReadOnlyArray<RelativeMemberInfo>,
   viewerID: ?string,
   usernamePrefix: string,
diff --git a/native/chat/chat-input-bar.react.js b/native/chat/chat-input-bar.react.js
--- a/native/chat/chat-input-bar.react.js
+++ b/native/chat/chat-input-bar.react.js
@@ -33,7 +33,7 @@
 } from 'lib/actions/thread-actions.js';
 import { createLoadingStatusSelector } from 'lib/selectors/loading-selectors.js';
 import { threadInfoSelector } from 'lib/selectors/thread-selectors.js';
-import { userStoreSearchIndex } from 'lib/selectors/user-selectors.js';
+import { userStoreMentionSearchIndex } from 'lib/selectors/user-selectors.js';
 import { colorIsDark } from 'lib/shared/color-utils.js';
 import { useEditMessage } from 'lib/shared/edit-messages-utils.js';
 import {
@@ -49,7 +49,7 @@
   messageKey,
   type MessagePreviewResult,
 } from 'lib/shared/message-utils.js';
-import SearchIndex from 'lib/shared/search-index.js';
+import SentencePrefixSearchIndex from 'lib/shared/sentence-prefix-search-index.js';
 import {
   threadHasPermission,
   viewerIsMember,
@@ -169,7 +169,7 @@
   +dispatchActionPromise: DispatchActionPromise,
   +joinThread: (request: ClientThreadJoinRequest) => Promise<ThreadJoinPayload>,
   +inputState: ?InputState,
-  +userSearchIndex: SearchIndex,
+  +userSearchIndex: SentencePrefixSearchIndex,
   +userMentionsCandidates: $ReadOnlyArray<RelativeMemberInfo>,
   +parentThreadInfo: ?ThreadInfo,
   +editedMessagePreview: ?MessagePreviewResult,
@@ -1270,7 +1270,7 @@
   const dispatchActionPromise = useDispatchActionPromise();
   const callJoinThread = useServerCall(joinThread);
 
-  const userSearchIndex = useSelector(userStoreSearchIndex);
+  const userSearchIndex = useSelector(userStoreMentionSearchIndex);
 
   const { parentThreadID } = props.threadInfo;
   const parentThreadInfo = useSelector(state =>
diff --git a/web/chat/chat-input-bar.react.js b/web/chat/chat-input-bar.react.js
--- a/web/chat/chat-input-bar.react.js
+++ b/web/chat/chat-input-bar.react.js
@@ -12,7 +12,7 @@
 import SWMansionIcon from 'lib/components/SWMansionIcon.react.js';
 import { createLoadingStatusSelector } from 'lib/selectors/loading-selectors.js';
 import { threadInfoSelector } from 'lib/selectors/thread-selectors.js';
-import { userStoreSearchIndex } from 'lib/selectors/user-selectors.js';
+import { userStoreMentionSearchIndex } from 'lib/selectors/user-selectors.js';
 import {
   getMentionTypeaheadUserSuggestions,
   getTypeaheadRegexMatches,
@@ -571,7 +571,7 @@
     const calendarQuery = useSelector(nonThreadCalendarQuery);
     const dispatchActionPromise = useDispatchActionPromise();
     const callJoinThread = useServerCall(joinThread);
-    const userSearchIndex = useSelector(userStoreSearchIndex);
+    const userSearchIndex = useSelector(userStoreMentionSearchIndex);
 
     const { parentThreadID } = props.threadInfo;
     const parentThreadInfo = useSelector(state =>