diff --git a/services/identity/src/database.rs b/services/identity/src/database.rs
--- a/services/identity/src/database.rs
+++ b/services/identity/src/database.rs
@@ -3,7 +3,9 @@
 use std::sync::Arc;
 
 use aws_sdk_dynamodb::model::AttributeValue;
-use aws_sdk_dynamodb::output::{GetItemOutput, PutItemOutput};
+use aws_sdk_dynamodb::output::{
+  GetItemOutput, PutItemOutput, UpdateItemOutput,
+};
 use aws_sdk_dynamodb::types::Blob;
 use aws_sdk_dynamodb::{Client, Error as DynamoDBError};
 use aws_types::sdk_config::SdkConfig;
@@ -79,14 +81,18 @@
     &self,
     user_id: String,
     registration: ServerRegistration<Cipher>,
-  ) -> Result<PutItemOutput, Error> {
+  ) -> Result<UpdateItemOutput, Error> {
     self
       .client
-      .put_item()
+      .update_item()
       .table_name(PAKE_USERS_TABLE)
-      .item(PAKE_USERS_TABLE_PARTITION_KEY, AttributeValue::S(user_id))
-      .item(
-        PAKE_USERS_TABLE_REGISTRATION_ATTRIBUTE,
+      .key(PAKE_USERS_TABLE_PARTITION_KEY, AttributeValue::S(user_id))
+      .update_expression(format!(
+        "SET {} :r",
+        PAKE_USERS_TABLE_REGISTRATION_ATTRIBUTE
+      ))
+      .expression_attribute_values(
+        ":r",
         AttributeValue::B(Blob::new(registration.serialize())),
       )
       .send()