diff --git a/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/boot/FastBootMetadataBuilder.java b/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/boot/FastBootMetadataBuilder.java
index 44ea98d385395..ab7a594f89bd2 100644
--- a/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/boot/FastBootMetadataBuilder.java
+++ b/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/boot/FastBootMetadataBuilder.java
@@ -255,6 +255,9 @@ private MergedSettings mergeSettings(PersistenceUnitDescriptor persistenceUnit)
         cfg.putIfAbsent(AvailableSettings.CONNECTION_HANDLING,
                 PhysicalConnectionHandlingMode.DELAYED_ACQUISITION_AND_RELEASE_BEFORE_TRANSACTION_COMPLETION);
 
+        // Auto-close sessions before transaction completion, as they should be when using JTA.
+        cfg.putIfAbsent(AvailableSettings.AUTO_CLOSE_SESSION, "true");
+
         if (readBooleanConfigurationValue(cfg, WRAP_RESULT_SETS)) {
             LOG.warn("Wrapping result sets is not supported. Setting " + WRAP_RESULT_SETS + " to false.");
         }
diff --git a/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/session/TransactionScopedSession.java b/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/session/TransactionScopedSession.java
index 3eafb8353c051..21c89cf29d9fe 100644
--- a/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/session/TransactionScopedSession.java
+++ b/extensions/hibernate-orm/runtime/src/main/java/io/quarkus/hibernate/orm/runtime/session/TransactionScopedSession.java
@@ -18,7 +18,6 @@
 import javax.persistence.criteria.CriteriaUpdate;
 import javax.persistence.metamodel.Metamodel;
 import javax.transaction.Status;
-import javax.transaction.Synchronization;
 import javax.transaction.TransactionManager;
 import javax.transaction.TransactionSynchronizationRegistry;
 
@@ -86,17 +85,13 @@ SessionResult acquireSession() {
             Session newSession = sessionFactory.openSession();
             newSession.joinTransaction();
             transactionSynchronizationRegistry.putResource(sessionKey, newSession);
-            transactionSynchronizationRegistry.registerInterposedSynchronization(new Synchronization() {
-                @Override
-                public void beforeCompletion() {
-                    newSession.flush();
-                }
-
-                @Override
-                public void afterCompletion(int i) {
-                    newSession.close();
-                }
-            });
+            // No need to flush or close the session upon transaction completion:
+            // Hibernate ORM itself registers a transaction that does just that.
+            // See:
+            // - io.quarkus.hibernate.orm.runtime.boot.FastBootMetadataBuilder.mergeSettings
+            // - org.hibernate.resource.transaction.backend.jta.internal.JtaTransactionCoordinatorImpl.joinJtaTransaction
+            // - org.hibernate.internal.SessionImpl.beforeTransactionCompletion
+            // - org.hibernate.internal.SessionImpl.afterTransactionCompletion
             return new SessionResult(newSession, false, true);
         } else {
             //this will throw an exception if the request scope is not active