diff --git a/src/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core/Extensions/TypeExtensions.cs b/src/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core/Extensions/TypeExtensions.cs
index cf2a7b6f..dc819056 100644
--- a/src/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core/Extensions/TypeExtensions.cs
+++ b/src/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core/Extensions/TypeExtensions.cs
@@ -460,8 +460,8 @@ public static Type GetUnderlyingType(this Type type)
             }
 
             if (type.IsOpenApiArray())
-            {
-                underlyingType = type.GetElementType() ?? type.GetGenericArguments()[0];
+            {
+                underlyingType = type.GetElementType() ?? (type.GetGenericArguments() != null && type.GetGenericArguments().Length > 0 ? type.GetGenericArguments()[0] : (type.BaseType.GetGenericArguments() != null && type.BaseType.GetGenericArguments().Length > 0 ? type.BaseType.GetGenericArguments()[0] :type.GetInterfaces()[0].GetGenericArguments()[0])) ;
             }
 
             if (type.IsOpenApiDictionary())
@@ -557,7 +557,7 @@ public static Type GetOpenApiSubType(this Type type)
 
             if (type.IsArrayType())
             {
-                return type.GetGenericArguments()[0];
+                return type.GetGenericArguments() != null && type.GetGenericArguments().Length > 0 ? type.GetGenericArguments()[0] : (type.BaseType.GetGenericArguments() != null && type.BaseType.GetGenericArguments().Length > 0 ? type.BaseType.GetGenericArguments()[0] : type.GetInterfaces()[0].GetGenericArguments()[0]);
             }
 
             return null;
diff --git a/test-integration/Microsoft.Azure.WebJobs.Extensions.OpenApi.Document.Tests/Get_ApplicationJson_ArrayObject_Tests.cs b/test-integration/Microsoft.Azure.WebJobs.Extensions.OpenApi.Document.Tests/Get_ApplicationJson_ArrayObject_Tests.cs
index da6a5a37..8b53ed96 100644
--- a/test-integration/Microsoft.Azure.WebJobs.Extensions.OpenApi.Document.Tests/Get_ApplicationJson_ArrayObject_Tests.cs
+++ b/test-integration/Microsoft.Azure.WebJobs.Extensions.OpenApi.Document.Tests/Get_ApplicationJson_ArrayObject_Tests.cs
@@ -76,6 +76,7 @@ public void Given_OpenApiDocument_Then_It_Should_Return_ComponentSchema(string @
         [DataRow("arrayObjectModel", "object", "decimalValue", "array")]
         [DataRow("arrayObjectModel", "object", "stringObjectValue", "array")]
         [DataRow("arrayObjectModel", "object", "objectArrayValue", "array")]
+        [DataRow("arrayObjectModel", "object", "nestedCollectionValue", "array")]
         public void Given_OpenApiDocument_Then_It_Should_Return_ComponentSchemaProperty(string @ref, string refType, string propertyName, string propertyType)
         {
             var properties = this._doc["components"]["schemas"][@ref]["properties"];
@@ -107,6 +108,7 @@ public void Given_OpenApiDocument_Then_It_Should_Return_ComponentSchemaPropertyI
         [DataTestMethod]
         [DataRow("arrayObjectModel", "object", "stringObjectValue", "array", "stringObjectModel")]
         [DataRow("arrayObjectModel", "object", "objectArrayValue", "array", "list_object")]
+        [DataRow("arrayObjectModel", "object", "nestedCollectionValue", "array", "collection_userDefine")]
         public void Given_OpenApiDocument_Then_It_Should_Return_ComponentSchemaPropertyItemReference(string @ref, string refType, string propertyName, string propertyType, string itemRef)
         {
             var items = this._doc["components"]["schemas"][@ref]["properties"][propertyName]["items"];
diff --git a/test-integration/Microsoft.Azure.WebJobs.Extensions.OpenApi.TestApp/Models/ArrayObjectModel.cs b/test-integration/Microsoft.Azure.WebJobs.Extensions.OpenApi.TestApp/Models/ArrayObjectModel.cs
index f7a0674b..2e06f3a9 100644
--- a/test-integration/Microsoft.Azure.WebJobs.Extensions.OpenApi.TestApp/Models/ArrayObjectModel.cs
+++ b/test-integration/Microsoft.Azure.WebJobs.Extensions.OpenApi.TestApp/Models/ArrayObjectModel.cs
@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 
 namespace Microsoft.Azure.WebJobs.Extensions.OpenApi.TestApp.Models
 {
@@ -14,5 +15,11 @@ public class ArrayObjectModel
         public ISet<StringObjectModel> StringObjectValue { get; set; }
 
         public List<object[]> ObjectArrayValue { get; set; }
+
+        public Collection_Udf NestedCollectionValue { get; set; } 
     }
+
+    public class UserDefine { }
+
+    public class Collection_Udf : Collection<Collection<UserDefine>> { }
 }
diff --git a/test/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Tests.Fakes/FakeAliasInheritanceModel.cs b/test/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Tests.Fakes/FakeAliasInheritanceModel.cs
new file mode 100644
index 00000000..b6f09bf4
--- /dev/null
+++ b/test/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Tests.Fakes/FakeAliasInheritanceModel.cs
@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Text;
+
+namespace Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Tests.Fakes
+{
+    public class FakeAliasInheritanceModel : Collection<Collection<FakeModel>>
+    {
+
+    }
+}
diff --git a/test/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Tests/Extensions/TypeExtensionsTests.cs b/test/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Tests/Extensions/TypeExtensionsTests.cs
index 0d6a81d7..04a76796 100644
--- a/test/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Tests/Extensions/TypeExtensionsTests.cs
+++ b/test/Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Tests/Extensions/TypeExtensionsTests.cs
@@ -1,6 +1,6 @@
 using System;
 using System.Collections.Generic;
-
+using System.Collections.ObjectModel;
 using FluentAssertions;
 
 using Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Abstractions;
@@ -119,6 +119,7 @@ public void Given_NullableType_When_GetUnderlyingType_Invoked_Then_It_Should_Ret
         [DataRow(typeof(List<int>), typeof(int))]
         [DataRow(typeof(List<bool>), typeof(bool))]
         [DataRow(typeof(List<FakeModel>), typeof(FakeModel))]
+        [DataRow(typeof(FakeAliasInheritanceModel), typeof(Collection<FakeModel>))]
         public void Given_ListType_When_GetUnderlyingType_Invoked_Then_It_Should_Return_Result(Type type, Type expected)
         {
             var result = TypeExtensions.GetUnderlyingType(type);