diff --git a/src/EditorFeatures/CSharpTest/ChangeSignature/ChangeSignatureTests.cs b/src/EditorFeatures/CSharpTest/ChangeSignature/ChangeSignatureTests.cs
index fbf17d5f22dc4cdb3ce41f45f3c320615cd665e6..2e077727b8e0499ae1d7938b21596d77c0172d9d 100644
--- a/src/EditorFeatures/CSharpTest/ChangeSignature/ChangeSignatureTests.cs
+++ b/src/EditorFeatures/CSharpTest/ChangeSignature/ChangeSignatureTests.cs
@@ -6,6 +6,7 @@
 using System.Xml.Linq;
 using Microsoft.CodeAnalysis.Editor.UnitTests.ChangeSignature;
 using Microsoft.CodeAnalysis.Test.Utilities;
+using Microsoft.CodeAnalysis.Test.Utilities.ChangeSignature;
 using Roslyn.Test.Utilities;
 using Xunit;
 
@@ -315,7 +316,7 @@ public class C3
             using (var testState = ChangeSignatureTestState.Create(XElement.Parse(workspaceXml)))
             {
                 testState.TestChangeSignatureOptionsService.IsCancelled = false;
-                testState.TestChangeSignatureOptionsService.UpdatedSignature = updatedSignature;
+                testState.TestChangeSignatureOptionsService.UpdatedSignature = updatedSignature.Select(i => new AddedParameterOrExistingIndex(i)).ToArray();
                 var result = testState.ChangeSignature();
 
                 Assert.True(result.Succeeded);
diff --git a/src/EditorFeatures/CSharpTest/ChangeSignature/ReorderParametersTests.InvocationErrors.cs b/src/EditorFeatures/CSharpTest/ChangeSignature/ReorderParametersTests.InvocationErrors.cs
index 2e51bf356c25ed6970c054357289ba4f2c5fa66a..641373d5235676aff82d42ad70bf203c24837e7b 100644
--- a/src/EditorFeatures/CSharpTest/ChangeSignature/ReorderParametersTests.InvocationErrors.cs
+++ b/src/EditorFeatures/CSharpTest/ChangeSignature/ReorderParametersTests.InvocationErrors.cs
@@ -43,10 +43,10 @@ public void Goo(int x, string y)
         }
 
         [WpfFact, Trait(Traits.Feature, Traits.Features.ChangeSignature)]
-        public async Task ReorderMethodParameters_InsufficientParameters_None()
+        public async Task ReorderMethodParameters_CanBeStartedEvenWithNoParameters()
         {
             var markup = @"class C { void $$M() { } }";
-            await TestChangeSignatureViaCommandAsync(LanguageNames.CSharp, markup, expectedSuccess: false, expectedErrorText: FeaturesResources.This_signature_does_not_contain_parameters_that_can_be_changed);
+            await TestChangeSignatureViaCommandAsync(LanguageNames.CSharp, markup, expectedSuccess: true);
         }
 
         [WpfFact, Trait(Traits.Feature, Traits.Features.ChangeSignature)]
diff --git a/src/EditorFeatures/TestUtilities/ChangeSignature/AbstractChangeSignatureTests.cs b/src/EditorFeatures/TestUtilities/ChangeSignature/AbstractChangeSignatureTests.cs
index af8ad730398d6941e923d56d662fa2b5b77ec20c..b938d12380ad6a308b448c7e91068b2e856ed31f 100644
--- a/src/EditorFeatures/TestUtilities/ChangeSignature/AbstractChangeSignatureTests.cs
+++ b/src/EditorFeatures/TestUtilities/ChangeSignature/AbstractChangeSignatureTests.cs
@@ -15,28 +15,29 @@
 
 namespace Microsoft.CodeAnalysis.Editor.UnitTests.ChangeSignature
 {
-    internal abstract class AbstractChangeSignatureTests : AbstractCodeActionTest
+    public abstract class AbstractChangeSignatureTests : AbstractCodeActionTest
     {
         protected override ParseOptions GetScriptOptions()
         {
             throw new NotSupportedException();
         }
 
-        public async Task TestChangeSignatureViaCodeActionAsync(
+        internal async Task TestChangeSignatureViaCodeActionAsync(
             string markup,
             bool expectedCodeAction = true,
             bool isCancelled = false,
             int[] updatedSignature = null,
             string expectedCode = null,
             int index = 0)
-            => await TestChangeSignatureViaCodeActionAsync(markup, expectedCodeAction, isCancelled,
-                updatedSignature.Select(i => new AddedParameterOrExistingIndex(i)).ToArray(), expectedCode, index).ConfigureAwait(false);
+            => await TestChangeSignatureViaCodeActionAsync(
+                markup, updatedSignature?.Select(i => new AddedParameterOrExistingIndex(i)).ToArray(),
+                expectedCodeAction, isCancelled, expectedCode, index).ConfigureAwait(false);
 
-        public async Task TestChangeSignatureViaCodeActionAsync(
+        internal async Task TestChangeSignatureViaCodeActionAsync(
             string markup,
+            AddedParameterOrExistingIndex[] updatedSignature,
             bool expectedCodeAction = true,
             bool isCancelled = false,
-            AddedParameterOrExistingIndex[] updatedSignature = null,
             string expectedCode = null,
             int index = 0)
         {
@@ -64,7 +65,7 @@ protected override ParseOptions GetScriptOptions()
             }
         }
 
-        public async Task TestChangeSignatureViaCommandAsync(
+        internal async Task TestChangeSignatureViaCommandAsync(
             string languageName,
             string markup,
             bool expectedSuccess = true,
@@ -75,20 +76,20 @@ protected override ParseOptions GetScriptOptions()
             bool verifyNoDiagnostics = false,
             ParseOptions parseOptions = null,
             int expectedSelectedIndex = -1)
-            => await TestChangeSignatureViaCommandAsync(languageName, markup, expectedSuccess,
-                updatedSignature.Select(i => new AddedParameterOrExistingIndex(i)).ToArray(),
-                expectedUpdatedInvocationDocumentCode,
+            => await TestChangeSignatureViaCommandAsync(languageName, markup,
+                updatedSignature?.Select(i => new AddedParameterOrExistingIndex(i)).ToArray(),
+                expectedSuccess, expectedUpdatedInvocationDocumentCode,
                 expectedErrorText,
                 totalParameters,
                 verifyNoDiagnostics,
                 parseOptions,
                 expectedSelectedIndex);
 
-        public async Task TestChangeSignatureViaCommandAsync(
+        internal async Task TestChangeSignatureViaCommandAsync(
             string languageName,
             string markup,
+            AddedParameterOrExistingIndex[] updatedSignature,
             bool expectedSuccess = true,
-            AddedParameterOrExistingIndex[] updatedSignature = null,
             string expectedUpdatedInvocationDocumentCode = null,
             string expectedErrorText = null,
             int? totalParameters = null,
diff --git a/src/EditorFeatures/TestUtilities/ChangeSignature/TestChangeSignatureOptionsService.cs b/src/EditorFeatures/TestUtilities/ChangeSignature/TestChangeSignatureOptionsService.cs
index 8dc7f4385088a72c63f5b59d388a3d3a9418f916..20deda19ec0c73f72fab5cd1bb3980ca389e6176 100644
--- a/src/EditorFeatures/TestUtilities/ChangeSignature/TestChangeSignatureOptionsService.cs
+++ b/src/EditorFeatures/TestUtilities/ChangeSignature/TestChangeSignatureOptionsService.cs
@@ -29,7 +29,7 @@ AddedParameterResult IChangeSignatureOptionsService.GetAddedParameter(Document d
             Document document)
         {
             var list = parameters.ToListOfParameters();
-            var updateParameters = UpdatedSignature.Select(item => item.IsExisting
+            var updateParameters = UpdatedSignature?.Select(item => item.IsExisting
             ? list[item.OldIndex]
             : item.AddedParameter).ToList();
 
diff --git a/src/Features/CSharp/Portable/ChangeSignature/CSharpChangeSignatureService.cs b/src/Features/CSharp/Portable/ChangeSignature/CSharpChangeSignatureService.cs
index 4a5bca58770ba82d4e8eac90baa20174e58c5933..4b3704d1691cea4190911d58c7648b4208eacbf3 100644
--- a/src/Features/CSharp/Portable/ChangeSignature/CSharpChangeSignatureService.cs
+++ b/src/Features/CSharp/Portable/ChangeSignature/CSharpChangeSignatureService.cs
@@ -390,11 +390,10 @@ private SyntaxNode GetNodeContainingTargetNode(SyntaxNode matchingNode)
                     isReducedExtensionMethod = true;
                 }
 
-
                 SignatureChange signaturePermutationWithoutAddedParameters = signaturePermutation.WithoutAddedParameters();
 
                 var newArguments = PermuteArgumentList(document, declarationSymbol, invocation.ArgumentList.Arguments, signaturePermutationWithoutAddedParameters, isReducedExtensionMethod);
-                newArguments = AddNewArgumentsToList(document, declarationSymbol, newArguments, signaturePermutation, isReducedExtensionMethod);
+                newArguments = AddNewArgumentsToList(newArguments, signaturePermutation);
                 return invocation.WithArgumentList(invocation.ArgumentList.WithArguments(newArguments).WithAdditionalAnnotations(changeSignatureFormattingAnnotation));
             }
 
@@ -449,7 +448,7 @@ private SyntaxNode GetNodeContainingTargetNode(SyntaxNode matchingNode)
             return null;
         }
 
-        private SeparatedSyntaxList<ArgumentSyntax> AddNewArgumentsToList(Document document, ISymbol declarationSymbol, SeparatedSyntaxList<ArgumentSyntax> newArguments, SignatureChange signaturePermutation, bool isReducedExtensionMethod)
+        private SeparatedSyntaxList<ArgumentSyntax> AddNewArgumentsToList(SeparatedSyntaxList<ArgumentSyntax> newArguments, SignatureChange signaturePermutation)
         {
             List<ArgumentSyntax> fullList = new List<ArgumentSyntax>();
 
@@ -473,12 +472,15 @@ private SeparatedSyntaxList<ArgumentSyntax> AddNewArgumentsToList(Document docum
                 }
                 else
                 {
-                    if (newArguments[indexInExistingList].NameColon != default)
+                    if (indexInExistingList < newArguments.Count)
                     {
-                        seenNameEquals = true;
-                    }
+                        if (newArguments[indexInExistingList].NameColon != default)
+                        {
+                            seenNameEquals = true;
+                        }
 
-                    fullList.Add(newArguments[indexInExistingList++]);
+                        fullList.Add(newArguments[indexInExistingList++]);
+                    }
                 }
             }