diff --git a/src/Tasks.UnitTests/RequiresFramework35SP1Assembly_Tests.cs b/src/Tasks.UnitTests/RequiresFramework35SP1Assembly_Tests.cs
new file mode 100644
index 00000000000..dbeb7412dc2
--- /dev/null
+++ b/src/Tasks.UnitTests/RequiresFramework35SP1Assembly_Tests.cs
@@ -0,0 +1,170 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Generic;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Tasks;
+using Microsoft.Build.Utilities;
+using Shouldly;
+using Xunit;
+
+namespace Microsoft.Build.UnitTests
+{
+    public sealed class RequiresFramework35SP1Assembly_Tests
+    {
+        private readonly ITestOutputHelper _output;
+
+        public RequiresFramework35SP1Assembly_Tests(ITestOutputHelper output)
+        {
+            _output = output;
+        }
+
+        private RequiresFramework35SP1Assembly CreateTask() =>
+            new()
+            {
+                BuildEngine = new MockEngine(_output),
+            };
+
+        [Fact]
+        public void Defaults_UncheckedSigningTriggers()
+        {
+            // The task's default SigningManifests=false is itself an "unchecked signing" trigger,
+            // so the all-defaults case reports RequiresMinimumFramework35SP1=true.
+            RequiresFramework35SP1Assembly task = CreateTask();
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeTrue();
+        }
+
+        [Fact]
+        public void SigningEnabled_NoOtherSignals_DoesNotTrigger()
+        {
+            RequiresFramework35SP1Assembly task = CreateTask();
+            task.SigningManifests = true;
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeFalse();
+        }
+
+        [Fact]
+        public void ErrorReportUrl_Triggers()
+        {
+            RequiresFramework35SP1Assembly task = CreateTask();
+            task.SigningManifests = true;
+            task.ErrorReportUrl = "https://example.com/errors";
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeTrue();
+        }
+
+        [Fact]
+        public void CreateDesktopShortcut_OnNet35_Triggers()
+        {
+            RequiresFramework35SP1Assembly task = CreateTask();
+            task.SigningManifests = true;
+            task.TargetFrameworkVersion = "v3.5";
+            task.CreateDesktopShortcut = true;
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeTrue();
+        }
+
+        [Fact]
+        public void SuiteName_Triggers()
+        {
+            RequiresFramework35SP1Assembly task = CreateTask();
+            task.SigningManifests = true;
+            task.SuiteName = "MyAppSuite";
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeTrue();
+        }
+
+        [Theory]
+        [InlineData("ReferencedAssemblies")]
+        [InlineData("Assemblies")]
+        [InlineData("Files")]
+        [InlineData("DeploymentManifestEntryPoint")]
+        [InlineData("EntryPoint")]
+        public void IncludeHashFalse_OnAnyItemInput_Triggers(string inputName)
+        {
+            RequiresFramework35SP1Assembly task = CreateTask();
+            task.SigningManifests = true;
+            ITaskItem item = new TaskItem("some.dll", new Dictionary<string, string?> { { "IncludeHash", "false" } });
+            AssignItemInput(task, inputName, item);
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeTrue();
+        }
+
+        [Fact]
+        public void CreateDesktopShortcut_OnNet20_DoesNotTrigger()
+        {
+            RequiresFramework35SP1Assembly task = CreateTask();
+            task.SigningManifests = true;
+            task.TargetFrameworkVersion = "v2.0";
+            task.CreateDesktopShortcut = true;
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeFalse();
+        }
+
+        [Fact]
+        public void CreateDesktopShortcut_BareVersionString_Works()
+        {
+            RequiresFramework35SP1Assembly task = CreateTask();
+            task.SigningManifests = true;
+            task.TargetFrameworkVersion = "3.5";
+            task.CreateDesktopShortcut = true;
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeTrue();
+        }
+
+        [Fact]
+        public void Sp1AssemblyIdentity_TriggersWithoutIncludeHash()
+        {
+            RequiresFramework35SP1Assembly task = CreateTask();
+            task.SigningManifests = true;
+            AssignItemInput(task, "Files", new TaskItem("System.Data.Entity"));
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeTrue();
+        }
+
+        [Fact]
+        public void Net35ClientSentinelIdentity_Triggers()
+        {
+            RequiresFramework35SP1Assembly task = CreateTask();
+            task.SigningManifests = true;
+            AssignItemInput(task, "Assemblies", new TaskItem("Sentinel.v3.5Client"));
+
+            task.Execute().ShouldBeTrue();
+            task.RequiresMinimumFramework35SP1.ShouldBeTrue();
+        }
+
+        private static void AssignItemInput(RequiresFramework35SP1Assembly task, string inputName, ITaskItem item)
+        {
+            switch (inputName)
+            {
+                case "ReferencedAssemblies":
+                    task.ReferencedAssemblies = [item];
+                    break;
+                case "Assemblies":
+                    task.Assemblies = [item];
+                    break;
+                case "Files":
+                    task.Files = [item];
+                    break;
+                case "DeploymentManifestEntryPoint":
+                    task.DeploymentManifestEntryPoint = item;
+                    break;
+                case "EntryPoint":
+                    task.EntryPoint = item;
+                    break;
+                default:
+                    throw new System.ArgumentOutOfRangeException(nameof(inputName));
+            }
+        }
+    }
+}
diff --git a/src/Tasks/RequiresFramework35SP1Assembly.cs b/src/Tasks/RequiresFramework35SP1Assembly.cs
index 391e28041b1..83d9cc827d5 100644
--- a/src/Tasks/RequiresFramework35SP1Assembly.cs
+++ b/src/Tasks/RequiresFramework35SP1Assembly.cs
@@ -12,6 +12,7 @@ namespace Microsoft.Build.Tasks
     /// <summary>
     /// This task determines if this project requires VS2008 SP1 assembly.
     /// </summary>
+    [MSBuildMultiThreadableTask]
     public sealed class RequiresFramework35SP1Assembly : TaskExtension
     {
         #region Fields