diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6fa32748ac..f1bbfb69d5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,11 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Removed
 - Removed the `Features` API which is not supported by OpenSearch from the low-level client ([#331](https://github.com/opensearch-project/opensearch-net/pull/331))
 
+
+### Fixed
+- Fixed `IEnumerable<int?>` property mapping. ([#380](https://github.com/opensearch-project/opensearch-net/pull/375))
+
+
 ### Dependencies
 - Bumps `Microsoft.CodeAnalysis.CSharp` from 4.2.0 to 4.6.0
 - Bumps `NSwag.Core.Yaml` from 13.19.0 to 13.20.0
@@ -118,4 +123,4 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 [Unreleased]: https://github.com/opensearch-project/opensearch-net/compare/v1.5.0...main
 [1.5.0]: https://github.com/opensearch-project/opensearch-net/compare/v1.4.0...v1.5.0
 [1.4.0]: https://github.com/opensearch-project/opensearch-net/compare/v1.3.0...v1.4.0
-[1.3.0]: https://github.com/opensearch-project/opensearch-net/compare/v1.2.0...v1.3.0
\ No newline at end of file
+[1.3.0]: https://github.com/opensearch-project/opensearch-net/compare/v1.2.0...v1.3.0
diff --git a/src/OpenSearch.Client/Mapping/Visitor/PropertyWalker.cs b/src/OpenSearch.Client/Mapping/Visitor/PropertyWalker.cs
index fcd72b7415..5734b2d21b 100644
--- a/src/OpenSearch.Client/Mapping/Visitor/PropertyWalker.cs
+++ b/src/OpenSearch.Client/Mapping/Visitor/PropertyWalker.cs
@@ -205,11 +205,25 @@ private static Type GetUnderlyingType(Type type)
 			if (type.IsArray)
 				return type.GetElementType();
 
-			if (type.IsGenericType && type.GetGenericArguments().Length == 1
-				&& (type.GetInterfaces().HasAny(t => t == typeof(IEnumerable)) || Nullable.GetUnderlyingType(type) != null))
-				return type.GetGenericArguments()[0];
+			if (ShouldUnwrapType(type))
+			{
+				var returnType = type.GetGenericArguments()[0];
+				if (ShouldUnwrapType(returnType)) // This is needed for types like IEnumerable<int?>.
+				{
+					return returnType.GetGenericArguments()[0];
+				}
+				return returnType;
+			}
 
 			return type;
 		}
+
+		private static bool ShouldUnwrapType(Type ty) =>
+					ty.IsGenericType &&
+					ty.GetGenericArguments().Length == 1 &&
+					(
+						ty.GetInterfaces().HasAny(t => t == typeof(IEnumerable)) ||
+						Nullable.GetUnderlyingType(ty) != null
+					);
 	}
 }
diff --git a/tests/Tests/Mapping/PropertyWalkerTests .cs b/tests/Tests/Mapping/PropertyWalkerTests .cs
new file mode 100644
index 0000000000..eaa5d91749
--- /dev/null
+++ b/tests/Tests/Mapping/PropertyWalkerTests .cs	
@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using FluentAssertions;
+using OpenSearch.Client;
+using OpenSearch.OpenSearch.Xunit.XunitPlumbing;
+
+namespace Tests.Mapping
+{
+	public class PropertyWalkerTests
+	{
+		[U]
+		public void BoolGetsMappedCorrectly()
+		{
+			var result = TestPropertyType<bool>();
+			result.Should().Be("boolean");
+		}
+
+		[U]
+		public void StringGetsMappedCorrectly()
+		{
+			var result = TestPropertyType<string>();
+			result.Should().Be("text");
+		}
+
+
+		[U]
+		public void DateTimeGetsMappedCorrectly()
+		{
+			var result = TestPropertyType<DateTime>();
+			result.Should().Be("date");
+		}
+
+		[U]
+		public void IEnumerableOfNullableGetsMappedCorrectly()
+		{
+			var result = TestPropertyType<IEnumerable<int?>>();
+			result.Should().Be("integer");
+		}
+
+		[U]
+		public void IListOfNullableGetsMappedCorrectly()
+		{
+			var result = TestPropertyType<IList<int?>>();
+			result.Should().Be("integer");
+		}
+
+		[U]
+		public void IEnumerableOfValueTypesGetsMappedCorrectly()
+		{
+			var result = TestPropertyType<IEnumerable<int>>();
+			result.Should().Be("integer");
+		}
+
+		[U]
+		public void IListOfValueTypesGetsMappedCorrectly()
+		{
+			var result = TestPropertyType<IList<int>>();
+			result.Should().Be("integer");
+		}
+
+		private static string TestPropertyType<T>()
+		{
+			var walker = new PropertyWalker(typeof(Test<T>), null, 0);
+			var properties = walker.GetProperties();
+			var result = properties.SingleOrDefault();
+			return result.Value?.Type;
+		}
+
+
+		private class Test<T>
+		{
+			public T Values { get; set; }
+		}
+
+	}
+}