diff --git a/hibernate-core/src/test/java/org/hibernate/orm/test/cid/CompositeIdAndMergeTest.java b/hibernate-core/src/test/java/org/hibernate/orm/test/cid/CompositeIdAndMergeTest.java
new file mode 100644
index 0000000000..9dc2d41e5b
--- /dev/null
+++ b/hibernate-core/src/test/java/org/hibernate/orm/test/cid/CompositeIdAndMergeTest.java
@@ -0,0 +1,162 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * Copyright Red Hat Inc. and Hibernate Authors
+ */
+package org.hibernate.orm.test.cid;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.JiraKey;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.junit.jupiter.api.Test;
+
+import jakarta.persistence.CascadeType;
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.IdClass;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.OneToMany;
+import jakarta.persistence.Table;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+@DomainModel(
+		annotatedClasses = {
+				CompositeIdAndMergeTest.Order.class,
+				CompositeIdAndMergeTest.Invoice.class,
+				CompositeIdAndMergeTest.LineItem.class
+		}
+)
+@SessionFactory
+@JiraKey("HHH-18131")
+public class CompositeIdAndMergeTest {
+
+	@Test
+	public void testMerge(SessionFactoryScope scope) {
+		Integer lineItemIndex = 2;
+		Order persistedOrder = scope.fromTransaction(
+				session -> {
+					Order order = new Order( "order" );
+					session.persist( order );
+
+					Invoice invoice = new Invoice( "invoice" );
+					LineItem lineItem = new LineItem( lineItemIndex );
+					invoice.addLine( lineItem );
+					order.setInvoice( invoice );
+
+					session.merge( order );
+					return order;
+				}
+		);
+
+		scope.inTransaction(
+				session -> {
+					Order order = session.find( Order.class, persistedOrder.getId() );
+					Invoice invoice = order.getInvoice();
+					assertThat( invoice ).isNotNull();
+					List<LineItem> lines = invoice.getLines();
+					assertThat( lines.size() ).isEqualTo( 1 );
+					assertThat( lines.get( 0 ).getIndex() ).isEqualTo( lineItemIndex );
+				}
+		);
+	}
+
+	@Entity(name = "Order")
+	@Table(name = "order_table")
+	public static class Order {
+		@Id
+		@GeneratedValue(strategy = GenerationType.IDENTITY)
+		private Long id;
+
+		@Column(nullable = false)
+		private String description;
+
+		@ManyToOne(cascade = { CascadeType.ALL })
+		private Invoice invoice;
+
+		public Order() {
+		}
+
+		public Order(String description) {
+			this.description = description;
+		}
+
+		public Long getId() {
+			return id;
+		}
+
+		public Invoice getInvoice() {
+			return invoice;
+		}
+
+		public void setInvoice(Invoice invoice) {
+			this.invoice = invoice;
+		}
+	}
+
+	@Entity(name = "Invoice")
+	public static class Invoice {
+		@Id
+		@GeneratedValue(strategy = GenerationType.IDENTITY)
+		private Long id;
+
+		@Column(name = "number_column")
+		private String number;
+
+		@OneToMany(mappedBy = "invoice", cascade = { CascadeType.ALL }, orphanRemoval = true)
+		private List<LineItem> lines = new ArrayList<>();
+
+		public Invoice() {
+		}
+
+		public Invoice(String number) {
+			this.number = number;
+		}
+
+		public void addLine(LineItem line) {
+			lines.add( line );
+			line.invoice = this;
+		}
+
+		public List<LineItem> getLines() {
+			return lines;
+		}
+	}
+
+	@Entity
+	@Table(name = "invoice_lines")
+	@IdClass(LineItemId.class)
+	public static class LineItem {
+		@Id
+		@ManyToOne
+		private Invoice invoice;
+
+		@Id
+		@Column(name = "index_column")
+		private Integer index;
+
+		public LineItem() {
+		}
+
+		public LineItem(Integer index) {
+			this.index = index;
+		}
+
+		public Integer getIndex() {
+			return index;
+		}
+	}
+
+	public static class LineItemId {
+		private Long invoice;
+		private Integer index;
+
+	}
+
+}