diff --git a/System.IO.Abstractions.TestingHelpers.Tests/MockFileSystemTests.cs b/System.IO.Abstractions.TestingHelpers.Tests/MockFileSystemTests.cs
index fec774718..75575da70 100644
--- a/System.IO.Abstractions.TestingHelpers.Tests/MockFileSystemTests.cs
+++ b/System.IO.Abstractions.TestingHelpers.Tests/MockFileSystemTests.cs
@@ -334,13 +334,22 @@ public void MockFileSystem_GetFiles_ThrowsArgumentExceptionForInvalidCharacters(
         [TestCase(@"C:\somepath")]
         public void MockFileSystem_DefaultState_CurrentDirectoryExists(string currentDirectory)
         {
-            var fs = new MockFileSystem(null, currentDirectory);
+            var fs = new MockFileSystem(null, XFS.Path(currentDirectory));
 
             var actualCurrentDirectory = fs.DirectoryInfo.FromDirectoryName(".");
 
             Assert.IsTrue(actualCurrentDirectory.Exists);
         }
 
+        [Test]
+        public void MockFileSystem_Constructor_ThrowsForNonRootedCurrentDirectory()
+        {
+            var ae = Assert.Throws<ArgumentException>(() =>
+                new MockFileSystem(null, "non-rooted")
+            );
+            Assert.AreEqual("currentDirectory", ae.ParamName);
+        }
+
         [Test]
         public void MockFileSystem_DefaultState_DefaultTempDirectoryExists()
         {
@@ -348,7 +357,7 @@ public void MockFileSystem_DefaultState_DefaultTempDirectoryExists()
 
             var mockFileSystem = new MockFileSystem();
             var mockFileSystemOverload = new MockFileSystem(null, string.Empty);
-            
+
             Assert.IsTrue(mockFileSystem.Directory.Exists(tempDirectory));
             Assert.IsTrue(mockFileSystemOverload.Directory.Exists(tempDirectory));
         }
diff --git a/System.IO.Abstractions.TestingHelpers/MockFileSystem.cs b/System.IO.Abstractions.TestingHelpers/MockFileSystem.cs
index d87331bcf..d70b6a7cd 100644
--- a/System.IO.Abstractions.TestingHelpers/MockFileSystem.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockFileSystem.cs
@@ -24,6 +24,10 @@ public MockFileSystem(IDictionary<string, MockFileData> files, string currentDir
             {
                 currentDirectory = XFS.Path(DEFAULT_CURRENT_DIRECTORY);
             }
+            else if (!System.IO.Path.IsPathRooted(currentDirectory))
+            {
+                throw new ArgumentException("Current directory needs to be rooted.", nameof(currentDirectory));
+            }
 
             var defaultTempDirectory = XFS.Path(TEMP_DIRECTORY);
 
@@ -31,7 +35,7 @@ public MockFileSystem(IDictionary<string, MockFileData> files, string currentDir
             pathVerifier = new PathVerifier(this);
             this.files = new Dictionary<string, MockFileData>(StringOperations.Comparer);
 
-            Path = new MockPath(this,defaultTempDirectory);
+            Path = new MockPath(this, defaultTempDirectory);
             File = new MockFile(this);
             Directory = new MockDirectory(this, currentDirectory);
             FileInfo = new MockFileInfoFactory(this);
@@ -53,7 +57,7 @@ public MockFileSystem(IDictionary<string, MockFileData> files, string currentDir
                 AddDirectory(currentDirectory);
             }
 
-            if (!FileExists(defaultTempDirectory)) 
+            if (!FileExists(defaultTempDirectory))
             {
                 AddDirectory(defaultTempDirectory);
             }
@@ -77,7 +81,7 @@ private string FixPath(string path, bool checkCaps = false)
             {
                 throw new ArgumentNullException(nameof(path), StringResources.Manager.GetString("VALUE_CANNOT_BE_NULL"));
             }
-            
+
             var pathSeparatorFixed = path.Replace(Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar);
             var fullPath = Path.GetFullPath(pathSeparatorFixed);
 
@@ -159,7 +163,7 @@ public void AddDirectory(string path)
             {
                 if (FileExists(fixedPath) &&
                     (GetFile(fixedPath).Attributes & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)
-                        throw CommonExceptions.AccessDenied(fixedPath);
+                    throw CommonExceptions.AccessDenied(fixedPath);
 
                 var lastIndex = 0;
                 var isUnc =
@@ -238,7 +242,7 @@ public void MoveDirectory(string sourcePath, string destPath)
                     .Where(p => StringOperations.StartsWith(p, sourcePath))
                     .ToList();
 
-                foreach(var path in affectedPaths)
+                foreach (var path in affectedPaths)
                 {
                     var newPath = StringOperations.Replace(path, sourcePath, destPath);
                     files[newPath] = files[path];
diff --git a/System.IO.Abstractions.TestingHelpers/MockUnixSupport.cs b/System.IO.Abstractions.TestingHelpers/MockUnixSupport.cs
index d96acd332..9753a4a79 100644
--- a/System.IO.Abstractions.TestingHelpers/MockUnixSupport.cs
+++ b/System.IO.Abstractions.TestingHelpers/MockUnixSupport.cs
@@ -6,7 +6,7 @@ public static class MockUnixSupport
     {
         private static readonly Regex pathTransform = new Regex(@"^[a-zA-Z]:(?<path>.*)$");
 
-        public static string Path(string path) => IsUnixPlatform()
+        public static string Path(string path) => path != null && IsUnixPlatform()
             ? pathTransform.Replace(path, "${path}").Replace(@"\", "/")
             : path;