diff --git a/.changeset/fuzzy-buttons-yawn.md b/.changeset/fuzzy-buttons-yawn.md
new file mode 100644
index 00000000000..5b93e8721d0
--- /dev/null
+++ b/.changeset/fuzzy-buttons-yawn.md
@@ -0,0 +1,5 @@
+---
+"@atproto/ozone": patch
+---
+
+Improve indexing for "chat.bsky.moderation.getMessageContext"
diff --git a/packages/ozone/src/api/chat/getMessageContext.ts b/packages/ozone/src/api/chat/getMessageContext.ts
index a0e70855215..476d5a8fd54 100644
--- a/packages/ozone/src/api/chat/getMessageContext.ts
+++ b/packages/ozone/src/api/chat/getMessageContext.ts
@@ -19,6 +19,8 @@ export default function (server: Server, ctx: AppContext) {
         .selectFrom('moderation_event')
         .select('id')
         .where('subjectMessageId', '=', params.messageId)
+        // uses "moderation_event_message_id_idx" index
+        .where('subjectMessageId', 'is not', null)
         .where('action', '=', 'tools.ozone.moderation.defs#modEventReport')
         .limit(1)
         .executeTakeFirst()
diff --git a/packages/ozone/src/db/migrations/20250211T132135150Z-moderation-event-message-partial-idx.ts b/packages/ozone/src/db/migrations/20250211T132135150Z-moderation-event-message-partial-idx.ts
new file mode 100644
index 00000000000..a3edc00891d
--- /dev/null
+++ b/packages/ozone/src/db/migrations/20250211T132135150Z-moderation-event-message-partial-idx.ts
@@ -0,0 +1,26 @@
+import { Kysely, sql } from 'kysely'
+
+// support lookup for chat.bsky.moderation.getMessageContext
+
+export async function up(db: Kysely<unknown>): Promise<void> {
+  // @NOTE: These queries should be run with the "CONCURRENTLY" option in
+  // production to avoid locking the table. This is not supported by Kysely.
+  await db.schema.dropIndex('moderation_event_message_id_index').execute()
+  await db.schema
+    .createIndex('moderation_event_message_id_idx')
+    .on('moderation_event')
+    // https://github.com/kysely-org/kysely/issues/302
+    .expression(
+      sql`"subjectMessageId") WHERE ("subjectMessageId" IS NOT NULL AND "action" = 'tools.ozone.moderation.defs#modEventReport'`,
+    )
+    .execute()
+}
+
+export async function down(db: Kysely<unknown>): Promise<void> {
+  await db.schema.dropIndex('moderation_event_message_id_idx').execute()
+  await db.schema
+    .createIndex('moderation_event_message_id_index')
+    .on('moderation_event')
+    .column('subjectMessageId')
+    .execute()
+}
diff --git a/packages/ozone/src/db/migrations/index.ts b/packages/ozone/src/db/migrations/index.ts
index 609f4366572..82923722c54 100644
--- a/packages/ozone/src/db/migrations/index.ts
+++ b/packages/ozone/src/db/migrations/index.ts
@@ -19,3 +19,4 @@ export * as _20241018T205730722Z from './20241018T205730722Z-setting'
 export * as _20241026T205730722Z from './20241026T205730722Z-add-hosting-status-to-subject-status'
 export * as _20241220T144630860Z from './20241220T144630860Z-stats-materialized-views'
 export * as _20250204T003647759Z from './20250204T003647759Z-add-subject-priority-score'
+export * as _20250211T132135150Z from './20250211T132135150Z-moderation-event-message-partial-idx'