diff --git a/core/src/main/java/dev/morphia/mapping/experimental/CollectionReference.java b/core/src/main/java/dev/morphia/mapping/experimental/CollectionReference.java
index b988cc3ac2e..8767ba84f77 100644
--- a/core/src/main/java/dev/morphia/mapping/experimental/CollectionReference.java
+++ b/core/src/main/java/dev/morphia/mapping/experimental/CollectionReference.java
@@ -12,6 +12,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.ListIterator;
 import java.util.Map;
@@ -28,9 +29,9 @@
  */
 @SuppressWarnings({"rawtypes", "unchecked"})
 public abstract class CollectionReference<C extends Collection> extends MorphiaReference<C> {
+    private final Map<String, List<Object>> collections = new HashMap<>();
     private EntityModel entityModel;
     private List ids;
-    private final Map<String, List<Object>> collections = new HashMap<>();
 
     CollectionReference(Datastore datastore, EntityModel entityModel, List ids) {
         super(datastore);
@@ -47,11 +48,6 @@ public abstract class CollectionReference<C extends Collection> extends MorphiaR
         }
     }
 
-    abstract void setValues(List ids);
-
-    protected CollectionReference() {
-    }
-
     static void collate(EntityModel valueType, Map<String, List<Object>> collections,
                         Object o) {
         final String collectionName;
@@ -72,6 +68,9 @@ static List register(Map<String, List<Object>> collections, String name) {
         return collections.computeIfAbsent(name, k -> new ArrayList<>());
     }
 
+    protected CollectionReference() {
+    }
+
     /**
      * Gets the referenced entities.  This may require at least one request to the server.
      *
@@ -79,11 +78,6 @@ static List register(Map<String, List<Object>> collections, String name) {
      */
     public abstract C get();
 
-    @Override
-    public Class<C> getType() {
-        return (Class<C>) entityModel.getType();
-    }
-
     @Override
     public List<Object> getIds() {
         List<Object> ids = new ArrayList<>(this.ids);
@@ -96,6 +90,11 @@ public List<Object> getIds() {
         return ids;
     }
 
+    @Override
+    public Class<C> getType() {
+        return (Class<C>) entityModel.getType();
+    }
+
     @Override
     final List<Object> getId(Mapper mapper, Datastore datastore, EntityModel entityModel) {
         if (ids == null) {
@@ -106,6 +105,10 @@ final List<Object> getId(Mapper mapper, Datastore datastore, EntityModel entityM
         return ids;
     }
 
+    abstract Collection<?> getValues();
+
+    abstract void setValues(List ids);
+
     private List<Object> extractIds(List<Object> list) {
         List<Object> ids = new ArrayList<>();
         list.forEach(i -> {
@@ -149,8 +152,6 @@ final List find() {
         return values;
     }
 
-    abstract Collection<?> getValues();
-
     Map<Object, Object> query(String collection, List<Object> collectionIds) {
 
         final Map<Object, Object> idMap = new HashMap<>();
@@ -162,7 +163,7 @@ Map<Object, Object> query(String collection, List<Object> collectionIds) {
                 idMap.put(getDatastore().getMapper().getId(entity), entity);
             }
 
-            if (!ignoreMissing() && idMap.size() != collectionIds.size()) {
+            if (!ignoreMissing() && idMap.size() != new HashSet<>(collectionIds).size()) {
                 throw new ReferenceException(
                     Sofia.missingReferencedEntities(entityModel.getType().getSimpleName()));
 
diff --git a/core/src/test/java/dev/morphia/test/mapping/lazy/TestLazyIdOnlyIgnoreMissing.java b/core/src/test/java/dev/morphia/test/mapping/lazy/TestLazyIdOnlyIgnoreMissing.java
index e5aa2cfe0c5..0d5b7ad0a53 100644
--- a/core/src/test/java/dev/morphia/test/mapping/lazy/TestLazyIdOnlyIgnoreMissing.java
+++ b/core/src/test/java/dev/morphia/test/mapping/lazy/TestLazyIdOnlyIgnoreMissing.java
@@ -1,16 +1,39 @@
 package dev.morphia.test.mapping.lazy;
 
 import dev.morphia.Datastore;
+import dev.morphia.annotations.Entity;
+import dev.morphia.annotations.Id;
 import dev.morphia.annotations.Reference;
 import dev.morphia.test.mapping.ProxyTestBase;
 import dev.morphia.test.models.TestEntity;
 import org.bson.types.ObjectId;
 import org.testng.annotations.Test;
 
+import java.util.List;
+import java.util.Objects;
+
 import static dev.morphia.query.experimental.filters.Filters.eq;
+import static org.testng.Assert.assertEquals;
 
 @Test(groups = "references")
 public class TestLazyIdOnlyIgnoreMissing extends ProxyTestBase {
+    @Test
+    public void testDuplicatesInList() {
+        getMapper().map(ListReferences.class, ReferencedEntity.class);
+        ListReferences references = new ListReferences();
+        ReferencedEntity entity1 = new ReferencedEntity();
+        entity1.foo = "1";
+        ReferencedEntity entity2 = new ReferencedEntity();
+        entity2.foo = "2";
+        getDs().save(List.of(entity1, entity2));
+        references.list = List.of(entity1, entity2, entity1);
+        getDs().save(references);
+
+        ListReferences first = getDs().find(ListReferences.class).first();
+
+        assertEquals(first, references);
+    }
+
     public void testSaveAfterReferentIsGone() {
         checkForProxyTypes();
 
@@ -47,6 +70,38 @@ public void testSaveAfterReferentIsGone() {
         datastore.save(root);
     }
 
+    @Entity
+    private static class ListReferences {
+        @Id
+        private ObjectId id;
+        @Reference
+        List<ReferencedEntity> list;
+
+        private ListReferences() {
+        }
+
+        private ListReferences(List<ReferencedEntity> list) {
+            this.list = list;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (!(o instanceof ListReferences)) {
+                return false;
+            }
+            ListReferences that = (ListReferences) o;
+            return Objects.equals(list, that.list) && Objects.equals(id, that.id);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(list, id);
+        }
+    }
+
     public static class ReferencedEntity extends TestEntity {
         private String foo;
 
@@ -57,6 +112,24 @@ public String getFoo() {
         public void setFoo(String string) {
             foo = string;
         }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(id, foo);
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (!(o instanceof ReferencedEntity)) {
+                return false;
+            }
+            ReferencedEntity that = (ReferencedEntity) o;
+            return Objects.equals(id, that.id)
+                   && Objects.equals(foo, that.foo);
+        }
     }
 
     public static class RootEntity extends TestEntity {