diff --git a/packages/runtime/src/client/crud/operations/base.ts b/packages/runtime/src/client/crud/operations/base.ts
index 975fd6e0..f27001fa 100644
--- a/packages/runtime/src/client/crud/operations/base.ts
+++ b/packages/runtime/src/client/crud/operations/base.ts
@@ -2083,7 +2083,7 @@ export abstract class BaseOperationHandler<Schema extends SchemaDef> {
         } else {
             // otherwise, create a new transaction and execute the callback
             let txBuilder = this.kysely.transaction();
-            txBuilder = txBuilder.setIsolationLevel(isolationLevel ?? TransactionIsolationLevel.RepeatableRead);
+            txBuilder = txBuilder.setIsolationLevel(isolationLevel ?? TransactionIsolationLevel.ReadCommitted);
             return txBuilder.execute(callback);
         }
     }
diff --git a/packages/runtime/src/client/executor/zenstack-query-executor.ts b/packages/runtime/src/client/executor/zenstack-query-executor.ts
index e1fb6298..a2005bff 100644
--- a/packages/runtime/src/client/executor/zenstack-query-executor.ts
+++ b/packages/runtime/src/client/executor/zenstack-query-executor.ts
@@ -90,7 +90,7 @@ export class ZenStackQueryExecutor<Schema extends SchemaDef> extends DefaultQuer
                 // mutations are wrapped in tx if not already in one
                 if (this.isMutationNode(compiledQuery.query) && !this.driver.isTransactionConnection(connection)) {
                     await this.driver.beginTransaction(connection, {
-                        isolationLevel: TransactionIsolationLevel.RepeatableRead,
+                        isolationLevel: TransactionIsolationLevel.ReadCommitted,
                     });
                     startedTx = true;
                 }