diff --git a/hibernate-core/src/main/java/org/hibernate/type/ManyToOneType.java b/hibernate-core/src/main/java/org/hibernate/type/ManyToOneType.java
index 3c27da133a2f..eefe40170f89 100644
--- a/hibernate-core/src/main/java/org/hibernate/type/ManyToOneType.java
+++ b/hibernate-core/src/main/java/org/hibernate/type/ManyToOneType.java
@@ -249,7 +249,7 @@ public boolean isDirty(
 		}
 		Object oldid = getIdentifier( old, session );
 		Object newid = getIdentifier( current, session );
-		return getIdentifierType( session ).isDirty( oldid, newid, session );
+		return getIdentifierOrUniqueKeyType( session.getFactory() ).isDirty( oldid, newid, session );
 	}
 
 	@Override
@@ -267,7 +267,7 @@ public boolean isDirty(
 			}
 			Object oldid = getIdentifier( old, session );
 			Object newid = getIdentifier( current, session );
-			return getIdentifierType( session ).isDirty( oldid, newid, checkable, session );
+			return getIdentifierOrUniqueKeyType( session.getFactory() ).isDirty( oldid, newid, checkable, session );
 		}
 		
 	}
diff --git a/hibernate-core/src/test/java/org/hibernate/orm/test/associations/ManyToOneUniqueKeyReferenceWithCustomIdTest.java b/hibernate-core/src/test/java/org/hibernate/orm/test/associations/ManyToOneUniqueKeyReferenceWithCustomIdTest.java
new file mode 100644
index 000000000000..b8d92ec659ee
--- /dev/null
+++ b/hibernate-core/src/test/java/org/hibernate/orm/test/associations/ManyToOneUniqueKeyReferenceWithCustomIdTest.java
@@ -0,0 +1,219 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.orm.test.associations;
+
+import java.io.Serializable;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Types;
+import java.util.Objects;
+
+import org.hibernate.HibernateException;
+import org.hibernate.annotations.NaturalId;
+import org.hibernate.annotations.Type;
+import org.hibernate.engine.spi.SharedSessionContractImplementor;
+import org.hibernate.usertype.EnhancedUserType;
+
+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.Entity;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.Id;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+
+/**
+ * @author Kowsar Atazadeh
+ */
+@SessionFactory
+@DomainModel(annotatedClasses =
+		{
+				ManyToOneUniqueKeyReferenceWithCustomIdTest.Phone.class,
+				ManyToOneUniqueKeyReferenceWithCustomIdTest.User.class
+		})
+@JiraKey("HHH-18764")
+public class ManyToOneUniqueKeyReferenceWithCustomIdTest {
+
+	@Test
+	void test(SessionFactoryScope scope) {
+		scope.inTransaction( session -> {
+			Phone phone = new Phone();
+
+			User user1 = new User( new CustomId( "u1" ), "Kowsar" );
+			session.persist( user1 );
+			phone.setUser( user1 );
+			session.persist( phone );
+
+			User user2 = new User( new CustomId( "u2" ), "Someone" );
+			session.persist( user2 );
+			phone.setUser( user2 );
+			session.persist( phone );
+		} );
+	}
+
+	@Entity(name = "Phone")
+	static class Phone {
+		@Id
+		@GeneratedValue
+		Long id;
+
+		@ManyToOne(fetch = FetchType.LAZY)
+		@JoinColumn(referencedColumnName = "name", nullable = false)
+		User user;
+
+		public Long getId() {
+			return id;
+		}
+
+		public void setId(Long id) {
+			this.id = id;
+		}
+
+		public User getUser() {
+			return user;
+		}
+
+		public void setUser(User user) {
+			this.user = user;
+		}
+	}
+
+	@Entity(name = "_User")
+	static class User {
+		@Id
+		@Type(CustomIdType.class)
+		CustomId id;
+
+		@NaturalId
+		String name;
+
+		public User() {
+		}
+
+		public User(CustomId id, String name) {
+			this.id = id;
+			this.name = name;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		public CustomId getId() {
+			return id;
+		}
+
+		public void setId(CustomId id) {
+			this.id = id;
+		}
+	}
+
+	static class CustomIdType implements EnhancedUserType<CustomId> {
+		@Override
+		public String toSqlLiteral(CustomId value) {
+			return "'" + value.toString() + "'";
+		}
+
+		@Override
+		public String toString(CustomId value) throws HibernateException {
+			return value.toString();
+		}
+
+		@Override
+		public void nullSafeSet(
+				PreparedStatement st, CustomId value, int position,
+				SharedSessionContractImplementor session) throws SQLException {
+			st.setObject( position, value.toString(), getSqlType() );
+		}
+
+		@Override
+		public CustomId nullSafeGet(ResultSet rs, int position, SharedSessionContractImplementor session, Object owner)
+				throws SQLException {
+			String idValue = rs.getString( position );
+			return idValue != null ? fromStringValue( idValue ) : null;
+		}
+
+		@Override
+		public CustomId fromStringValue(CharSequence sequence) throws HibernateException {
+			return new CustomId( sequence.toString() );
+		}
+
+		@Override
+		public int getSqlType() {
+			return Types.VARCHAR;
+		}
+
+		@Override
+		public Class<CustomId> returnedClass() {
+			return CustomId.class;
+		}
+
+		@Override
+		public CustomId deepCopy(CustomId value) {
+			return new CustomId( value.getId() );
+		}
+
+		@Override
+		public boolean isMutable() {
+			return false;
+		}
+
+		@Override
+		public Serializable disassemble(CustomId value) {
+			return value;
+		}
+
+		@Override
+		public CustomId assemble(Serializable cached, Object owner) {
+			return (CustomId) cached;
+		}
+
+		@Override
+		public boolean equals(CustomId x, CustomId y) {
+			return Objects.equals( x, y );
+		}
+
+		@Override
+		public int hashCode(CustomId x) {
+			return x != null ? x.hashCode() : 0;
+		}
+	}
+
+	static class CustomId implements Serializable {
+		private String id;
+
+		public CustomId() {
+		}
+
+		public CustomId(String id) {
+			this.id = id;
+		}
+
+		@Override
+		public String toString() {
+			return id;
+		}
+
+		public String getId() {
+			return id;
+		}
+
+		public void setId(String id) {
+			this.id = id;
+		}
+	}
+}