diff --git a/test/unit/Elsa.Workflows.Core.UnitTests/Models/JsonActivityConstructorContextHelperTests.cs b/test/unit/Elsa.Workflows.Core.UnitTests/Models/JsonActivityConstructorContextHelperTests.cs
new file mode 100644
index 000000000..fe9f84b94
--- /dev/null
+++ b/test/unit/Elsa.Workflows.Core.UnitTests/Models/JsonActivityConstructorContextHelperTests.cs
@@ -0,0 +1,77 @@
+
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Elsa.Workflows.Models;
+
+namespace Elsa.Workflows.Core.UnitTests.Models;
+
+public sealed class JsonActivityConstructorContextHelperTests
+{
+    private static readonly JsonSerializerOptions _serializerOptions = new();
+
+    [Theory]
+    [InlineData("_Metadata")]
+    [InlineData("Metadata")]
+    [InlineData("_CustomProperties")]
+    [InlineData("CustomProperties")]
+    public void When_InputName_Is_ReservedKeyWord_Then_ThrowsException_WhenReadingInputs(string reservedInputName)
+    {
+        // Arrange
+        var activityDescriptor = new ActivityDescriptor
+        {
+            Inputs =
+            [
+                new() 
+                { 
+                    Name = reservedInputName, 
+                    Type = typeof(object),
+                    IsSynthetic = true
+                }
+            ]
+        };
+        var jsonElement = GetJsonElementWithReservedInputName(reservedInputName);
+
+        // Act & Assert
+        Assert.Throws<KeyNotFoundException>(() =>
+        {
+            _ = JsonActivityConstructorContextHelper.CreateActivity<WorkflowAsActivity>(
+                activityDescriptor,
+                jsonElement,
+                _serializerOptions
+            );
+        });
+    }
+
+    private static JsonElement GetJsonElementWithReservedInputName(string inputName)
+    {
+        const string json = "{\"workflowDefinitionId\":\"Id\",\"id\":\"Id\",\"nodeId\":\"NodeId\",\"name\":\"Workflow-as-activity\",\"type\":\"WorkflowAsActivity\",\"customProperties\":{\"canStartWorkflow\":false,\"runAsynchronously\":false},\"metadata\":{\"designer\":{\"position\":{\"x\":1525.99609375,\"y\":171.5625},\"size\":{\"width\":230.4296875,\"height\":68.4375}},\"displayText\":\"Test\"},\"<inputName>\":{\"typeName\":\"Object\",\"expression\":{\"type\":\"JavaScript\",\"value\":\"return {\\n    \\u0022key\\u0022 : obj.value\\n}\"},\"memoryReference\":{\"id\":\"memref:input--name\"}}}";
+        var jsonWithInputName = json.Replace("<inputName>", inputName);
+        return JsonElement.Parse(jsonWithInputName);
+    }
+
+    private class WorkflowAsActivity : IActivity
+    {
+        public string Id { get; set; } = "Id";
+        public string NodeId { get; set; } = "NodeId";
+        public string? Name { get; set; } = "Workflow-as-activity";
+        public string Type { get; set; } = "WorkflowAsActivity";
+        public int Version { get; set; } = 1;
+
+        [JsonIgnore]
+        public IDictionary<string, object> CustomProperties { get; set; } = new Dictionary<string, object>();
+        public IDictionary<string, object> SyntheticProperties { get; set; } = new Dictionary<string, object>();
+
+        [JsonIgnore]
+        public IDictionary<string, object> Metadata { get; set; } = new Dictionary<string, object>();
+
+        public ValueTask<bool> CanExecuteAsync(ActivityExecutionContext context)
+        {
+            return new(true);
+        }
+
+        public ValueTask ExecuteAsync(ActivityExecutionContext context)
+        {
+            return new();
+        }
+    }
+}