diff --git a/src/Build.UnitTests/BackEnd/TaskBuilder_Tests.cs b/src/Build.UnitTests/BackEnd/TaskBuilder_Tests.cs
index 7748a189690..1e6b56edd0e 100644
--- a/src/Build.UnitTests/BackEnd/TaskBuilder_Tests.cs
+++ b/src/Build.UnitTests/BackEnd/TaskBuilder_Tests.cs
@@ -596,6 +596,31 @@ public void NullMetadataOnLegacyOutputItems()
             logger.AssertLogContains("[foo: ]");
         }
 
+        /// <summary>
+        /// If an item returned from a task has bare-minimum metadata implementation, we shouldn't crash.
+        /// </summary>
+        [Fact]
+        public void MinimalLegacyOutputItems()
+        {
+            string customTaskPath = Assembly.GetExecutingAssembly().Location;
+
+            string projectContents = $"""
+                                     <Project>
+                                       <UsingTask TaskName="TaskThatReturnsMinimalItem" AssemblyFile="{customTaskPath}" />
+
+                                       <Target Name="Build">
+                                         <TaskThatReturnsMinimalItem>
+                                           <Output TaskParameter="MinimalTaskItemOutput" ItemName="Outputs"/>
+                                         </TaskThatReturnsMinimalItem>
+
+                                         <Message Text="[%(Outputs.Identity): %(Outputs.a)]" Importance="High" />
+                                       </Target>
+                                     </Project>
+                                     """;
+
+            MockLogger logger = ObjectModelHelpers.BuildProjectExpectSuccess(projectContents, _testOutput, LoggerVerbosity.Diagnostic);
+        }
+
         /// <summary>
         /// Regression test for https://github.com/dotnet/msbuild/issues/5080
         /// </summary>
diff --git a/src/Build.UnitTests/TaskThatReturnsMinimalItem.cs b/src/Build.UnitTests/TaskThatReturnsMinimalItem.cs
new file mode 100644
index 00000000000..7f8eec32b2a
--- /dev/null
+++ b/src/Build.UnitTests/TaskThatReturnsMinimalItem.cs
@@ -0,0 +1,48 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections;
+
+using Microsoft.Build.Framework;
+
+namespace Microsoft.Build.Engine.UnitTests;
+
+/// <summary>
+/// Task that emulates .NET 3.5 tasks.
+/// </summary>
+public sealed class TaskThatReturnsMinimalItem : ITask
+{
+    public IBuildEngine? BuildEngine { get; set; }
+    public ITaskHost? HostObject { get; set; }
+
+    [Output]
+    public ITaskItem MinimalTaskItemOutput { get => new MinimalTaskItem(); }
+
+    public bool Execute() => true;
+
+    /// <summary>
+    /// Minimal implementation of <see cref="ITaskItem"/> that uses a <see cref="Hashtable"/> for metadata,
+    /// like MSBuild 3 did.
+    /// </summary>
+    internal sealed class MinimalTaskItem : ITaskItem
+    {
+        public string ItemSpec { get => $"{nameof(MinimalTaskItem)}spec"; set => throw new NotImplementedException(); }
+
+        public ICollection MetadataNames => throw new NotImplementedException();
+
+        public int MetadataCount => throw new NotImplementedException();
+
+        public IDictionary CloneCustomMetadata()
+        {
+            Hashtable t = new();
+            t["key"] = "value";
+
+            return t;
+        }
+        public void CopyMetadataTo(ITaskItem destinationItem) => throw new NotImplementedException();
+        public string GetMetadata(string metadataName) => "value";
+        public void RemoveMetadata(string metadataName) => throw new NotImplementedException();
+        public void SetMetadata(string metadataName, string metadataValue) => throw new NotImplementedException();
+    }
+}
diff --git a/src/Build/BackEnd/TaskExecutionHost/TaskExecutionHost.cs b/src/Build/BackEnd/TaskExecutionHost/TaskExecutionHost.cs
index 69da00e3955..705ca12979e 100644
--- a/src/Build/BackEnd/TaskExecutionHost/TaskExecutionHost.cs
+++ b/src/Build/BackEnd/TaskExecutionHost/TaskExecutionHost.cs
@@ -1396,8 +1396,8 @@ private void GatherTaskItemOutputs(bool outputTargetIsItem, string outputTargetN
                                     newItem = new ProjectItemInstance(_projectInstance, outputTargetName, EscapingUtilities.Escape(output.ItemSpec), parameterLocationEscaped);
 
                                     newItem.SetMetadataOnTaskOutput(output.CloneCustomMetadata()
-                                        .Cast<KeyValuePair<string, string>>()
-                                        .Select(x => new KeyValuePair<string, string>(x.Key, EscapingUtilities.Escape(x.Value))));
+                                        .Cast<DictionaryEntry>()
+                                        .Select(x => new KeyValuePair<string, string>((string)x.Key, EscapingUtilities.Escape((string)x.Value))));
                                 }
                             }
 
diff --git a/src/Framework/ITaskItemExtensions.cs b/src/Framework/ITaskItemExtensions.cs
index 7dc7dbdaf86..6ba56e1a880 100644
--- a/src/Framework/ITaskItemExtensions.cs
+++ b/src/Framework/ITaskItemExtensions.cs
@@ -35,7 +35,9 @@ public static IEnumerable<KeyValuePair<string, string>> EnumerateMetadata(this I
                 return enumerableMetadata;
             }
 
-            // In theory this should never be reachable.
+            // Fallback for
+            //  * ITaskItem implementations from MSBuild 3.5 from the GAC
+            //  * Custom ITaskItems that don't use Dictionary<string,string>
             var list = new KeyValuePair<string, string>[customMetadata.Count];
             int i = 0;