diff --git a/src/StringExtensions.cs b/src/StringExtensions.cs
index b4d5665..31b2480 100644
--- a/src/StringExtensions.cs
+++ b/src/StringExtensions.cs
@@ -11,6 +11,16 @@ namespace StringResourceVisualizer
 {
     public static class StringExtensions
     {
+        /// <summary>
+        /// Whether a file name is that of a Visual Studio solution file: the .sln format or the newer, XML based, .slnx format.
+        /// </summary>
+        public static bool IsSolutionFileName(this string fileName)
+        {
+            return !string.IsNullOrEmpty(fileName)
+                && (fileName.EndsWith(".sln", StringComparison.InvariantCultureIgnoreCase)
+                    || fileName.EndsWith(".slnx", StringComparison.InvariantCultureIgnoreCase));
+        }
+
         public static async Task<int> IndexOfAnyAsync(this string source, params string[] values)
         {
             try
diff --git a/src/StringResVizPackage.cs b/src/StringResVizPackage.cs
index 2f5100d..0ff024c 100644
--- a/src/StringResVizPackage.cs
+++ b/src/StringResVizPackage.cs
@@ -270,7 +270,7 @@ private async Task SetUpRunningDocumentTableEventsAsync(CancellationToken cancel
 		private void WatchForSolutionOrProjectChanges(string solutionFileName)
 		{
 			// It might actually be the project file name if no solution file exists
-			if (solutionFileName.EndsWith(".sln", StringComparison.InvariantCultureIgnoreCase))
+			if (solutionFileName.IsSolutionFileName())
 			{
 				this.SlnWatcher.Filter = Path.GetFileName(solutionFileName);
 				this.SlnWatcher.Path = Path.GetDirectoryName(solutionFileName);
@@ -315,7 +315,7 @@ private async void SlnWatcher_Renamed(object sender, RenamedEventArgs e)
 			try
 			{
 				// Don't want to know about temporary files created during save.
-				if (e.FullPath.EndsWith(".sln"))
+				if (e.FullPath.IsSolutionFileName())
 				{
 					await this.SetOrUpdateListOfResxFilesAsync(Path.GetDirectoryName(e.FullPath));
 				}
diff --git a/src/StringResourceVisualizer.Tests/StringExtensionsTests.cs b/src/StringResourceVisualizer.Tests/StringExtensionsTests.cs
new file mode 100644
index 0000000..466c279
--- /dev/null
+++ b/src/StringResourceVisualizer.Tests/StringExtensionsTests.cs
@@ -0,0 +1,73 @@
+// <copyright file="StringExtensionsTests.cs" company="Matt Lacey">
+// Copyright (c) Matt Lacey. All rights reserved.
+// </copyright>
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace StringResourceVisualizer.Tests
+{
+    [TestClass]
+    public class StringExtensionsTests
+    {
+        [TestMethod]
+        public void IsSolutionFileName_Sln()
+        {
+            TestIt(@"C:\Source\MyApp\MyApp.sln", true);
+        }
+
+        [TestMethod]
+        public void IsSolutionFileName_Slnx()
+        {
+            TestIt(@"C:\Source\MyApp\MyApp.slnx", true);
+        }
+
+        [TestMethod]
+        public void IsSolutionFileName_Sln_UpperCase()
+        {
+            TestIt(@"C:\Source\MyApp\MyApp.SLN", true);
+        }
+
+        [TestMethod]
+        public void IsSolutionFileName_Slnx_MixedCase()
+        {
+            TestIt(@"C:\Source\MyApp\MyApp.SlnX", true);
+        }
+
+        [TestMethod]
+        public void IsSolutionFileName_ProjectFile()
+        {
+            TestIt(@"C:\Source\MyApp\MyApp.csproj", false);
+        }
+
+        [TestMethod]
+        public void IsSolutionFileName_SolutionFilter()
+        {
+            TestIt(@"C:\Source\MyApp\MyApp.slnf", false);
+        }
+
+        [TestMethod]
+        public void IsSolutionFileName_ExtensionInTheMiddleOfThePath()
+        {
+            TestIt(@"C:\Source\MyApp.sln\readme.txt", false);
+        }
+
+        [TestMethod]
+        public void IsSolutionFileName_Empty()
+        {
+            TestIt(string.Empty, false);
+        }
+
+        [TestMethod]
+        public void IsSolutionFileName_Null()
+        {
+            TestIt(null, false);
+        }
+
+        private void TestIt(string input, bool expected)
+        {
+            var actual = input.IsSolutionFileName();
+
+            Assert.AreEqual(expected, actual);
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/StringResourceVisualizer.Tests/StringResourceVisualizer.Tests.csproj b/src/StringResourceVisualizer.Tests/StringResourceVisualizer.Tests.csproj
index 82e550c..d77d350 100644
--- a/src/StringResourceVisualizer.Tests/StringResourceVisualizer.Tests.csproj
+++ b/src/StringResourceVisualizer.Tests/StringResourceVisualizer.Tests.csproj
@@ -44,6 +44,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="ResourceAdornmentManagerTests.cs" />
+    <Compile Include="StringExtensionsTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>
   <ItemGroup>