diff --git a/core/src/sessions/in_memory_session_service.ts b/core/src/sessions/in_memory_session_service.ts
index d505b64f..ad4d9529 100644
--- a/core/src/sessions/in_memory_session_service.ts
+++ b/core/src/sessions/in_memory_session_service.ts
@@ -174,6 +174,10 @@ export class InMemorySessionService extends BaseSessionService {
     session,
     event,
   }: AppendEventRequest): Promise<Event> {
+    if (event.partial) {
+      return event;
+    }
+
     await super.appendEvent({session, event});
     session.lastUpdateTime = event.timestamp;
 
diff --git a/core/test/sessions/in_memory_session_service_test.ts b/core/test/sessions/in_memory_session_service_test.ts
index eeed7f4b..e766e1d8 100644
--- a/core/test/sessions/in_memory_session_service_test.ts
+++ b/core/test/sessions/in_memory_session_service_test.ts
@@ -264,6 +264,31 @@ describe('InMemorySessionService', () => {
       expect(retrievedSession?.lastUpdateTime).toBe(timestamp);
     });
 
+    it('ignores partial events without updating the session', async () => {
+      const session = await service.createSession({
+        appName: 'app',
+        userId: 'user',
+      });
+      const initialUpdateTime = session.lastUpdateTime;
+      const partialEvent = createEvent({
+        partial: true,
+        timestamp: initialUpdateTime + 1000,
+      });
+
+      await service.appendEvent({session, event: partialEvent});
+
+      expect(session.events).toEqual([]);
+      expect(session.lastUpdateTime).toBe(initialUpdateTime);
+
+      const retrievedSession = await service.getSession({
+        appName: 'app',
+        userId: 'user',
+        sessionId: session.id,
+      });
+      expect(retrievedSession?.events).toEqual([]);
+      expect(retrievedSession?.lastUpdateTime).toBe(initialUpdateTime);
+    });
+
     it('updates app state', async () => {
       const appName = 'app';
       const userId = 'user';