diff --git a/src/@types/PushRules.ts b/src/@types/PushRules.ts
index 7b436d85a85..da3b01b6d17 100644
--- a/src/@types/PushRules.ts
+++ b/src/@types/PushRules.ts
@@ -64,8 +64,6 @@ export enum ConditionKind {
     EventMatch = "event_match",
     EventPropertyIs = "event_property_is",
     EventPropertyContains = "event_property_contains",
-    IsUserMention = "org.matrix.msc3952.is_user_mention",
-    IsRoomMention = "org.matrix.msc3952.is_room_mention",
     ContainsDisplayName = "contains_display_name",
     RoomMemberCount = "room_member_count",
     SenderNotificationPermission = "sender_notification_permission",
@@ -96,14 +94,6 @@ export interface IEventPropertyContainsCondition extends IPushRuleCondition<Cond
     value: string | boolean | null | number;
 }
 
-export interface IIsUserMentionCondition extends IPushRuleCondition<ConditionKind.IsUserMention> {
-    // no additional fields
-}
-
-export interface IIsRoomMentionCondition extends IPushRuleCondition<ConditionKind.IsRoomMention> {
-    // no additional fields
-}
-
 export interface IContainsDisplayNameCondition extends IPushRuleCondition<ConditionKind.ContainsDisplayName> {
     // no additional fields
 }
@@ -131,8 +121,6 @@ export type PushRuleCondition =
     | IEventMatchCondition
     | IEventPropertyIsCondition
     | IEventPropertyContainsCondition
-    | IIsUserMentionCondition
-    | IIsRoomMentionCondition
     | IContainsDisplayNameCondition
     | IRoomMemberCountCondition
     | ISenderNotificationPermissionCondition
diff --git a/src/pushprocessor.ts b/src/pushprocessor.ts
index 9674450b33e..4d85227fe82 100644
--- a/src/pushprocessor.ts
+++ b/src/pushprocessor.ts
@@ -27,8 +27,6 @@ import {
     IEventMatchCondition,
     IEventPropertyIsCondition,
     IEventPropertyContainsCondition,
-    IIsRoomMentionCondition,
-    IIsUserMentionCondition,
     IPushRule,
     IPushRules,
     IRoomMemberCountCondition,
@@ -51,8 +49,6 @@ const RULEKINDS_IN_ORDER = [
     PushRuleKind.Underride,
 ];
 
-const MENTIONS_FIELD = "org.matrix.msc3952.mentions";
-
 // The default override rules to apply to the push rules that arrive from the server.
 // We do this for two reasons:
 //   1. Synapse is unlikely to send us the push rule in an incremental sync - see
@@ -391,10 +387,6 @@ export class PushProcessor {
                 return this.eventFulfillsEventPropertyIsCondition(cond, ev);
             case ConditionKind.EventPropertyContains:
                 return this.eventFulfillsEventPropertyContains(cond, ev);
-            case ConditionKind.IsUserMention:
-                return this.eventFulfillsUserMentionCondition(cond, ev);
-            case ConditionKind.IsRoomMention:
-                return this.eventFulfillsRoomMentionCondition(cond, ev);
             case ConditionKind.ContainsDisplayName:
                 return this.eventFulfillsDisplayNameCondition(cond, ev);
             case ConditionKind.RoomMemberCount:
@@ -470,50 +462,6 @@ export class PushProcessor {
         }
     }
 
-    private eventFulfillsUserMentionCondition(cond: IIsUserMentionCondition, ev: MatrixEvent): boolean {
-        const content = ev.getContent();
-        // Ensure the mentions field exists as an object and contains a user_ids
-        // field which is an array.
-        if (
-            !content ||
-            !content[MENTIONS_FIELD] ||
-            typeof content[MENTIONS_FIELD] != "object" ||
-            !content[MENTIONS_FIELD].user_ids ||
-            !Array.isArray(content[MENTIONS_FIELD].user_ids)
-        ) {
-            return false;
-        }
-
-        // Ensure the user is still in the room.
-        // XXX Why do we do this?
-        const room = this.client.getRoom(ev.getRoomId());
-        const userId = this.client.credentials.userId!;
-        const member = room?.currentState?.getMember(userId);
-        if (!member) {
-            return false;
-        }
-
-        return content[MENTIONS_FIELD].user_ids.includes(userId);
-    }
-
-    private eventFulfillsRoomMentionCondition(cond: IIsRoomMentionCondition, ev: MatrixEvent): boolean {
-        const content = ev.getContent();
-        // Ensure the mentions field exists as an object and contains a room
-        // field which is a boolean.
-        if (
-            !content ||
-            !content[MENTIONS_FIELD] ||
-            typeof content[MENTIONS_FIELD] != "object" ||
-            !content[MENTIONS_FIELD].room ||
-            typeof content[MENTIONS_FIELD].user_ids != "boolean"
-        ) {
-            return false;
-        }
-
-        // This must be a boolean, so can just return it directly.
-        return content[MENTIONS_FIELD].room;
-    }
-
     private eventFulfillsDisplayNameCondition(cond: IContainsDisplayNameCondition, ev: MatrixEvent): boolean {
         let content = ev.getContent();
         if (ev.isEncrypted() && ev.getClearContent()) {