diff --git a/Casbin.UnitTests/Fixtures/TestModelFixture.cs b/Casbin.UnitTests/Fixtures/TestModelFixture.cs
index 6c9e66a..7fc800d 100644
--- a/Casbin.UnitTests/Fixtures/TestModelFixture.cs
+++ b/Casbin.UnitTests/Fixtures/TestModelFixture.cs
@@ -16,6 +16,9 @@ public class TestModelFixture
     public static readonly string BasicWithoutUserPolicyText = ReadTestFile("basic_without_users_policy.csv");
     public static readonly string BasicWithRootModelText = ReadTestFile("basic_with_root_model.conf");
 
+    public static readonly string SaaRbacModelText = ReadTestFile("saa_model.conf");
+    public static readonly string SaaRbacPolicyText = ReadTestFile("saa_rbac_policy.csv");
+
     public static readonly string RbacPolicyText = ReadTestFile("rbac_policy.csv");
     public static readonly string RbacCommentText = ReadTestFile("rbac_comment.conf");
     public static readonly string RbacInOperatorModelText = ReadTestFile("rbac_in_operator_model.conf");
@@ -119,6 +122,8 @@ public static IModel GetNewPriorityExplicitTestModel() =>
     public static IModel GetNewPriorityExplicitDenyOverrideModel() => GetNewTestModel(PriorityExplicitDenyOverrideModelText,
         PriorityExplicitDenyOverridePolicyText);
 
+    public static IModel GetNewSaaRbacTestModel() => GetNewTestModel(SaaRbacModelText, SaaRbacPolicyText);
+
     public static IModel GetNewRbacTestModel() => GetNewTestModel(RbacModelText, RbacPolicyText);
 
     public static IModel GetNewRbacWithDenyTestModel() => GetNewTestModel(RbacWithDenyModelText, RbacWithDenyPolicyText);
diff --git a/Casbin.UnitTests/ModelTests/ManagementApiTest.cs b/Casbin.UnitTests/ModelTests/ManagementApiTest.cs
index adf92b6..b4d45a7 100644
--- a/Casbin.UnitTests/ModelTests/ManagementApiTest.cs
+++ b/Casbin.UnitTests/ModelTests/ManagementApiTest.cs
@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Linq;
 using System.Threading.Tasks;
 using Casbin.Model;
 using Casbin.UnitTests.Extensions;
@@ -323,6 +324,46 @@ public async Task TestModifyPolicyAsync()
         Assert.False(res);
     }
 
+    private static List<List<string>> GenerateGroupingRules(int numberOfItems)
+    {
+        var groupingRules = new List<List<string>>();
+
+        for (int i = 1; i <= numberOfItems; i++)
+        {
+            string parent = $"Parent{i}";
+            string child = $"Child{i}";
+            groupingRules.Add(new List<string> { parent, child });
+        }
+
+        return groupingRules;
+    }
+
+    [Fact]
+    public void TestConcurrentModifyGroupingPolicy()
+    {
+        Enforcer e = new(TestModelFixture.GetNewSaaRbacTestModel());
+        e.BuildRoleLinks();
+
+        // Arrange
+        var policiesBeforeAct = e.GetNamedGroupingPolicy(PermConstants.GroupingPolicyType2).ToArray();
+        Assert.Empty(policiesBeforeAct);
+
+        var groupingRules = GenerateGroupingRules(1000);
+
+        Task.WaitAll(groupingRules.Select(rule => Task.Run(() =>
+        {
+            bool result = e.AddNamedGroupingPolicies(PermConstants.GroupingPolicyType2, new List<List<string>> { rule });
+            Assert.True(result);
+        })).ToArray());
+
+        // Assert
+        var policiesAfterAct = e.GetNamedGroupingPolicy(PermConstants.GroupingPolicyType2).ToArray();
+        foreach (var policy in groupingRules)
+        {
+            Assert.Contains(policy, policiesAfterAct);
+        }
+    }
+
     [Fact]
     public void TestModifyGroupingPolicy()
     {
diff --git a/Casbin.UnitTests/examples/saa_model.conf b/Casbin.UnitTests/examples/saa_model.conf
new file mode 100644
index 0000000..97b862c
--- /dev/null
+++ b/Casbin.UnitTests/examples/saa_model.conf
@@ -0,0 +1,17 @@
+[request_definition]
+# request includes subject, domain parent of obj, object requesting access for, action requested
+r = sub, dom, obj, act
+
+[policy_definition]
+p = sub, dom, act
+
+[role_definition]
+g = _, _
+g2 = _, _
+g3 = _, _
+
+[policy_effect]
+e = some(where (p.eft == allow))
+
+[matchers]
+m = g(r.sub, p.sub) && (g2(r.dom, p.dom) || r.obj == p.dom) && g3(r.act, p.act)
diff --git a/Casbin.UnitTests/examples/saa_rbac_policy.csv b/Casbin.UnitTests/examples/saa_rbac_policy.csv
new file mode 100644
index 0000000..2362ee1
--- /dev/null
+++ b/Casbin.UnitTests/examples/saa_rbac_policy.csv
@@ -0,0 +1,3 @@
+# sample policy, not needed for test
+p, tellers, banks/1, wager-editor
+
diff --git a/Casbin/Model/DefaultPolicyStore.Node.cs b/Casbin/Model/DefaultPolicyStore.Node.cs
index 8c469e3..e44e96d 100644
--- a/Casbin/Model/DefaultPolicyStore.Node.cs
+++ b/Casbin/Model/DefaultPolicyStore.Node.cs
@@ -34,7 +34,17 @@ public IReadOnlyList<IPolicyValues> SetPolicy(List<IPolicyValues> valuesList) =>
             Interlocked.Exchange(ref Policy, valuesList);
 
         public bool ContainsPolicy(IPolicyValues values)
-            => PolicyTextSet.Contains(values.ToText());
+        {
+            Lock.EnterReadLock();
+            try
+            {
+                return PolicyTextSet.Contains(values.ToText());
+            }
+            finally
+            {
+                Lock.ExitReadLock();
+            }
+        }
 
         public bool ValidatePolicy(IPolicyValues values)
         {
@@ -67,13 +77,13 @@ public bool TryAddPolicy(IPolicyValues values)
             try
             {
                 Policy.Add(values);
+                PolicyTextSet.Add(values.ToText());
             }
             finally
             {
                 Lock.ExitWriteLock();
             }
 
-            PolicyTextSet.Add(values.ToText());
             return true;
         }
 
@@ -244,13 +254,13 @@ bool LastLessOrEqualPriority(IPolicyValues v)
             {
                 int lastIndex = Policy.FindLastIndex(LastLessOrEqualPriority);
                 Policy.Insert(lastIndex + 1, values);
+                PolicyTextSet.Add(values.ToText());
             }
             finally
             {
                 Lock.ExitWriteLock();
             }
 
-            PolicyTextSet.Add(values.ToText());
             return true;
         }