diff --git a/src/XrmMockup365/Internal/EntityMatcher.cs b/src/XrmMockup365/Internal/EntityMatcher.cs
index f6964fb3..69d216ea 100644
--- a/src/XrmMockup365/Internal/EntityMatcher.cs
+++ b/src/XrmMockup365/Internal/EntityMatcher.cs
@@ -126,6 +126,10 @@ private static bool Matches(object attr, ConditionOperator op, IEnumerable<objec
                     return DateTimeCompareNow(attr, op, values);
 
                 case ConditionOperator.In:
+                    if (values != null && attr is OptionSetValueCollection optionSetValueCollection)
+                    {
+                        return string.Join(",", values.OrderBy(_ => _)) == string.Join(",", optionSetValueCollection.ToList().Select(_ => _.Value).OrderBy(_ => _));
+                    }
                     return values.Contains(ValueConverter.ConvertTo(attr, values.FirstOrDefault()?.GetType()));
 
                 case ConditionOperator.NotIn:
diff --git a/tests/XrmMockup365Test/TestFetchConditionOperators.cs b/tests/XrmMockup365Test/TestFetchConditionOperators.cs
index 34d1c077..51d2ee7a 100644
--- a/tests/XrmMockup365Test/TestFetchConditionOperators.cs
+++ b/tests/XrmMockup365Test/TestFetchConditionOperators.cs
@@ -3,6 +3,8 @@
 using Microsoft.Xrm.Sdk;
 using Microsoft.Xrm.Sdk.Query;
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using Xunit;
 namespace DG.XrmMockupTest
 {
@@ -10,6 +12,127 @@ public class TestFetchConditionOperators : UnitTestBase
     {
         public TestFetchConditionOperators(XrmMockupFixture fixture) : base(fixture)
         {
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item2 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item3 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item4 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.checkmark });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item2 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item3 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item4 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item3 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item4 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item3, Account_dg_Multiselect.Item4 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item3 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item4 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item3, Account_dg_Multiselect.Item4 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item3, Account_dg_Multiselect.Item4 });
+            CreateAccount(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item3, Account_dg_Multiselect.Item4 });
+
+            void CreateAccount(List<Account_dg_Multiselect> list)
+            {
+                for (int i = 0; i < 2; i++)
+                {
+                    list.Reverse();
+                    var account = new Account();
+                    account.dg_Multiselect = list;
+                    account.Id = orgAdminUIService.Create(account);
+                }
+            }
+        }
+
+        private class MultiselectCases : TheoryData<List<Account_dg_Multiselect>>
+        {
+            public MultiselectCases()
+            {
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item2 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item3 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item4 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item2 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item3 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item4 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item3 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item4 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item3, Account_dg_Multiselect.Item4 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item3 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item4 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item3, Account_dg_Multiselect.Item4 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item3, Account_dg_Multiselect.Item4 });
+                Add(new List<Account_dg_Multiselect> { Account_dg_Multiselect.Item1, Account_dg_Multiselect.Item2, Account_dg_Multiselect.Item3, Account_dg_Multiselect.Item4 });
+            }
+        }
+
+        [Theory]
+        [ClassData(typeof(MultiselectCases))]
+        public void TestMultiselectConditionOperatorIn(List<Account_dg_Multiselect> optionSetValueCollection)
+        {
+            using (var context = new Xrm(orgAdminUIService))
+            {
+                var optionSetValues = optionSetValueCollection.Select(_ => (int)_).ToList();
+                for (int i = 0; i < 2; i++)
+                {
+                    optionSetValues.Reverse();
+                    string values = string.Empty;
+                    foreach (var value in optionSetValues)
+                    {
+                        values += $"<value>{value}</value>";
+                    }
+
+                    var fetchXml =
+                    $@"<fetch mapping='logical' version='1.0'>
+                        <entity name='account'>
+                            <filter>
+                                <condition attribute='dg_multiselect' operator='in'>
+                                    {values}
+                                </condition>
+                            </filter>
+                        </entity>
+                    </fetch>";
+                    EntityCollection result = Fetch(fetchXml);
+                    Assert.Equal(2, result.Entities.Count);
+                }
+            }
+        }
+
+        [Theory]
+        [ClassData(typeof(MultiselectCases))]
+        public void TestMultiselectConditionOperatorNotIn(List<Account_dg_Multiselect> optionSetValueCollection)
+        {
+            using (var context = new Xrm(orgAdminUIService))
+            {
+                var fetchXmlCount =
+                    $@"<fetch mapping='logical' version='1.0'>
+                        <entity name='account'>
+                            <attribute name='name' />
+                        </entity>
+                    </fetch>";
+                var count = Fetch(fetchXmlCount).Entities.Count;
+                var optionSetValues = optionSetValueCollection.Select(_ => (int)_).ToList();
+                for (int i = 0; i < 2; i++)
+                {
+                    optionSetValues.Reverse();
+                    string values = string.Empty;
+                    foreach (var value in optionSetValues)
+                    {
+                        values += $"<value>{value}</value>";
+                    }
+
+                    var fetchXml =
+                    $@"<fetch mapping='logical' version='1.0'>
+                        <entity name='account'>
+                            <filter>
+                                <condition attribute='dg_multiselect' operator='not-in'>
+                                    {values}
+                                </condition>
+                            </filter>
+                        </entity>
+                    </fetch>";
+                    EntityCollection result = Fetch(fetchXml);
+                    Assert.Equal(count - 2, result.Entities.Count);
+                }
+            }
         }
 
         [Theory]
diff --git a/tests/XrmMockup365Test/TestFormulaFields.cs b/tests/XrmMockup365Test/TestFormulaFields.cs
index 577f316c..cc537649 100644
--- a/tests/XrmMockup365Test/TestFormulaFields.cs
+++ b/tests/XrmMockup365Test/TestFormulaFields.cs
@@ -54,26 +54,36 @@ public async TTask CanEvaluateExpressionWithRelatedEntity()
         [ClassData(typeof(FunctionCases))]
         public async TTask CanEvaluateFunction(string formula, object expected)
         {
-            var evaluator = new FormulaFieldEvaluator(serviceFactory);
-            var result = await evaluator.Evaluate(formula, new Account(), TimeSpan.Zero);
-
-            if (result is ErrorValue error && expected is string errorString)
-            {
-                var errorMessage = string.Join("\n", error.Errors.Select(e => e.Message));
-                Assert.Contains(errorString, errorMessage);
-            }
-            else if (result is DateTime resultDateTime)
+            var targetCulture = new CultureInfo("en-US");
+            var originalUICulture = CultureInfo.CurrentUICulture;
+            try
             {
-                var expectedDateTime = (expected is DateTime dt)
-                    ? dt
-                    : (expected is "DateTime.Now")
-                        ? DateTime.Now
-                        : throw new InvalidOperationException("Expected value is not a DateTime or 'DateTime.Now'");
+                CultureInfo.CurrentUICulture = targetCulture;
+                var evaluator = new FormulaFieldEvaluator(serviceFactory);
+                var result = await evaluator.Evaluate(formula, new Account(), TimeSpan.Zero);
+
+                if (result is ErrorValue error && expected is string errorString)
+                {
+                    var errorMessage = string.Join("\n", error.Errors.Select(e => e.Message));
+                    Assert.Contains(errorString, errorMessage);
+                }
+                else if (result is DateTime resultDateTime)
+                {
+                    var expectedDateTime = (expected is DateTime dt)
+                        ? dt
+                        : (expected is "DateTime.Now")
+                            ? DateTime.Now
+                            : throw new InvalidOperationException("Expected value is not a DateTime or 'DateTime.Now'");
                     Assert.Equal(expectedDateTime, resultDateTime, TimeSpan.FromSeconds(1));
+                }
+                else
+                {
+                    Assert.Equal(expected, result);
+                }
             }
-            else
+            finally
             {
-                Assert.Equal(expected, result);
+                CultureInfo.CurrentUICulture = originalUICulture;
             }
         }