diff --git a/mem0/vector_stores/s3_vectors.py b/mem0/vector_stores/s3_vectors.py
index c44ce15c8..1c56c7884 100644
--- a/mem0/vector_stores/s3_vectors.py
+++ b/mem0/vector_stores/s3_vectors.py
@@ -122,7 +122,37 @@ class S3Vectors(VectorStoreBase):
         )
 
     def update(self, vector_id, vector=None, payload=None):
-        # S3 Vectors uses put_vectors for updates (overwrite)
+        # S3 Vectors uses put_vectors for updates (overwrite).
+        # When vector=None (e.g. metadata-only update triggered by event=NONE),
+        # fetch the existing vector data first to avoid passing None to boto3
+        # which causes a parameter validation error:
+        #   "Invalid type for parameter vectors[0].data.float32, value: None"
+        if vector is None:
+            existing = self.get(vector_id)
+            if existing is None:
+                logger.warning(f"update called with vector=None but {vector_id} not found; skipping")
+                return
+            try:
+                response = self.client.get_vectors(
+                    vectorBucketName=self.vector_bucket_name,
+                    indexName=self.collection_name,
+                    keys=[vector_id],
+                    returnData=True,
+                    returnMetadata=True,
+                )
+                vectors = response.get("vectors", [])
+                if not vectors:
+                    logger.warning(f"update: no vector data found for {vector_id}; skipping")
+                    return
+                vector = vectors[0].get("data", {}).get("float32")
+                if vector is None:
+                    logger.warning(f"update: float32 data is None for {vector_id}; skipping")
+                    return
+                if payload is None:
+                    payload = existing.payload
+            except Exception as e:
+                logger.error(f"update: failed to fetch existing vector for {vector_id}: {e}")
+                return
         self.insert(vectors=[vector], payloads=[payload], ids=[vector_id])
 
     def get(self, vector_id) -> Optional[OutputData]: