diff --git a/LiteDB.Tests/Issues/Issue2112_Tests.cs b/LiteDB.Tests/Issues/Issue2112_Tests.cs
new file mode 100644
index 000000000..2917c6bb0
--- /dev/null
+++ b/LiteDB.Tests/Issues/Issue2112_Tests.cs
@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Generic;
+using Xunit;
+using System.Linq;
+
+namespace LiteDB.Tests.Issues
+{
+    public class Issue2112_Tests
+    {
+        private BsonMapper _mapper = new BsonMapper();
+
+        [Fact]
+        public void Serialize_covariant_collection_has_type()
+        {
+            IA a = new A { Bs = new List<B> { new B() } };
+
+            var docA = _mapper.Serialize<IA>(a).AsDocument;
+            var docB = docA["Bs"].AsArray[0].AsDocument;
+
+            Assert.True(docA.ContainsKey("_type"));
+            Assert.True(docB.ContainsKey("_type"));
+        }
+
+        [Fact]
+        public void Deserialize_covariant_collection_succeed()
+        {
+            IA a = new A { Bs = new List<B> { new B() } };
+            var serialized = _mapper.Serialize<IA>(a);
+
+            var deserialized = _mapper.Deserialize<IA>(serialized);
+
+            Assert.Equal(1, deserialized.Bs.Count);
+        }
+
+        interface IA
+        {
+            // at runtime this will be a List<B>
+            IReadOnlyCollection<IB> Bs { get; set; }
+        }
+
+        class A : IA
+        {
+            public IReadOnlyCollection<IB> Bs { get; set; }
+        }
+
+        interface IB 
+        {
+
+        }
+
+        class B : IB 
+        {
+
+        }
+    }
+}
diff --git a/LiteDB/Client/Mapper/BsonMapper.Serialize.cs b/LiteDB/Client/Mapper/BsonMapper.Serialize.cs
index ed26073b6..1e013b16c 100644
--- a/LiteDB/Client/Mapper/BsonMapper.Serialize.cs
+++ b/LiteDB/Client/Mapper/BsonMapper.Serialize.cs
@@ -135,7 +135,7 @@ internal BsonValue Serialize(Type type, object obj, int depth)
             // check if is a list or array
             else if (obj is IEnumerable)
             {
-                return this.SerializeArray(Reflection.GetListItemType(obj.GetType()), obj as IEnumerable, depth);
+                return this.SerializeArray(Reflection.GetListItemType(type), obj as IEnumerable, depth);
             }
             // otherwise serialize as a plain object
             else