diff --git a/src/Runner.Worker/ActionRunner.cs b/src/Runner.Worker/ActionRunner.cs
index 8331e9915..b0c245ac3 100644
--- a/src/Runner.Worker/ActionRunner.cs
+++ b/src/Runner.Worker/ActionRunner.cs
@@ -143,8 +143,10 @@ namespace GitHub.Runner.Worker
             var templateEvaluator = ExecutionContext.ToPipelineTemplateEvaluator();
             var inputs = templateEvaluator.EvaluateStepInputs(Action.Inputs, ExecutionContext.ExpressionValues, ExecutionContext.ExpressionFunctions);
 
+            var userInputs = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
             foreach (KeyValuePair<string, string> input in inputs)
             {
+                userInputs.Add(input.Key);
                 string message = "";
                 if (definition.Data?.Deprecated?.TryGetValue(input.Key, out message) == true)
                 {
@@ -152,13 +154,15 @@ namespace GitHub.Runner.Worker
                 }
             }
 
+            var validInputs = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
             // Merge the default inputs from the definition
             if (definition.Data?.Inputs != null)
             {
                 var manifestManager = HostContext.GetService<IActionManifestManager>();
-                foreach (var input in (definition.Data?.Inputs))
+                foreach (var input in definition.Data.Inputs)
                 {
                     string key = input.Key.AssertString("action input name").Value;
+                    validInputs.Add(key);
                     if (!inputs.ContainsKey(key))
                     {
                         inputs[key] = manifestManager.EvaluateDefaultInput(ExecutionContext, key, input.Value);
@@ -166,6 +170,14 @@ namespace GitHub.Runner.Worker
                 }
             }
 
+            foreach (var input in userInputs)
+            {
+                if (!validInputs.Contains(input))
+                {
+                    ExecutionContext.Warning($"Unexpected input '{input}', valid inputs are ['{string.Join("', '", validInputs)}']");
+                }
+            }
+
             // Load the action environment.
             ExecutionContext.Debug("Loading env");
             var environment = new Dictionary<String, String>(VarUtil.EnvironmentVariableKeyComparer);
diff --git a/src/Test/L0/Worker/ActionRunnerL0.cs b/src/Test/L0/Worker/ActionRunnerL0.cs
index 24ff73f4f..73f215a3f 100644
--- a/src/Test/L0/Worker/ActionRunnerL0.cs
+++ b/src/Test/L0/Worker/ActionRunnerL0.cs
@@ -278,6 +278,59 @@ namespace GitHub.Runner.Common.Tests.Worker
             Assert.Equal("${{ matrix.node }}", _actionRunner.DisplayName);
         }
 
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public async void WarnInvalidInputs()
+        {
+            //Arrange
+            Setup();
+            var actionId = Guid.NewGuid();
+            var actionInputs = new MappingToken(null, null, null);
+            actionInputs.Add(new StringToken(null, null, null, "input1"), new StringToken(null, null, null, "test1"));
+            actionInputs.Add(new StringToken(null, null, null, "input2"), new StringToken(null, null, null, "test2"));
+            actionInputs.Add(new StringToken(null, null, null, "invalid1"), new StringToken(null, null, null, "invalid1"));
+            actionInputs.Add(new StringToken(null, null, null, "invalid2"), new StringToken(null, null, null, "invalid2"));
+            var action = new Pipelines.ActionStep()
+            {
+                Name = "action",
+                Id = actionId,
+                Reference = new Pipelines.ContainerRegistryReference()
+                {
+                    Image = "ubuntu:16.04"
+                },
+                Inputs = actionInputs
+            };
+
+            _actionRunner.Action = action;
+
+            Dictionary<string, string> finialInputs = new Dictionary<string, string>();
+            _handlerFactory.Setup(x => x.Create(It.IsAny<IExecutionContext>(), It.IsAny<ActionStepDefinitionReference>(), It.IsAny<IStepHost>(), It.IsAny<ActionExecutionData>(), It.IsAny<Dictionary<string, string>>(), It.IsAny<Dictionary<string, string>>(), It.IsAny<Variables>(), It.IsAny<string>()))
+                           .Callback((IExecutionContext executionContext, Pipelines.ActionStepDefinitionReference actionReference, IStepHost stepHost, ActionExecutionData data, Dictionary<string, string> inputs, Dictionary<string, string> environment, Variables runtimeVariables, string taskDirectory) =>
+                           {
+                               finialInputs = inputs;
+                           })
+                           .Returns(new Mock<IHandler>().Object);
+
+            //Act
+            await _actionRunner.RunAsync();
+
+            foreach (var input in finialInputs)
+            {
+                _hc.GetTrace().Info($"Input: {input.Key}={input.Value}");
+            }
+
+            //Assert
+            Assert.Equal("test1", finialInputs["input1"]);
+            Assert.Equal("test2", finialInputs["input2"]);
+            Assert.Equal("github", finialInputs["input3"]);
+            Assert.Equal("invalid1", finialInputs["invalid1"]);
+            Assert.Equal("invalid2", finialInputs["invalid2"]);
+
+            _ec.Verify(x => x.AddIssue(It.Is<Issue>(s => s.Message.Contains("Unexpected input 'invalid1'")), It.IsAny<string>()), Times.Once);
+            _ec.Verify(x => x.AddIssue(It.Is<Issue>(s => s.Message.Contains("Unexpected input 'invalid2'")), It.IsAny<string>()), Times.Once);
+        }
+
         private void Setup([CallerMemberName] string name = "")
         {
             _ecTokenSource?.Dispose();