diff --git a/src/Main/Base/Project/Src/Gui/Pads/ProjectBrowser/TreeNodes/DirectoryNode.cs b/src/Main/Base/Project/Src/Gui/Pads/ProjectBrowser/TreeNodes/DirectoryNode.cs
index 20533abafb..194886a2a3 100644
--- a/src/Main/Base/Project/Src/Gui/Pads/ProjectBrowser/TreeNodes/DirectoryNode.cs
+++ b/src/Main/Base/Project/Src/Gui/Pads/ProjectBrowser/TreeNodes/DirectoryNode.cs
@@ -474,6 +474,9 @@ namespace ICSharpCode.SharpDevelop.Project
 			if (!FileService.CheckFileName(newName)) {
 				return;
 			}
+			if (!FileService.CheckDirectoryName(newName)) {
+				return;
+			}
 			string oldText = Text;
 			Text = newName;
 			if (Directory != null) {
diff --git a/src/Main/Base/Project/Src/Services/File/FileService.cs b/src/Main/Base/Project/Src/Services/File/FileService.cs
index 12b28c3f94..aa2b538409 100644
--- a/src/Main/Base/Project/Src/Services/File/FileService.cs
+++ b/src/Main/Base/Project/Src/Services/File/FileService.cs
@@ -50,6 +50,18 @@ namespace ICSharpCode.Core
 			return false;
 		}
 		
+		/// <summary>
+		/// Checks that a single directory name is valid.
+		/// </summary>
+		/// <param name="name">A single directory name not the full path</param>
+		public static bool CheckDirectoryName(string name)
+		{
+			if (FileUtility.IsValidDirectoryName(name))
+				return true;
+			MessageService.ShowMessage(StringParser.Parse("${res:ICSharpCode.SharpDevelop.Commands.SaveFile.InvalidFileNameError}", new string[,] {{"FileName", name}}));
+			return false;
+		}
+		
 		class LoadFileWrapper
 		{
 			IDisplayBinding binding;
diff --git a/src/Main/Core/Project/Src/Services/FileUtility/FileUtility.cs b/src/Main/Core/Project/Src/Services/FileUtility/FileUtility.cs
index 6a7f7bd368..9732e213e7 100644
--- a/src/Main/Core/Project/Src/Services/FileUtility/FileUtility.cs
+++ b/src/Main/Core/Project/Src/Services/FileUtility/FileUtility.cs
@@ -315,6 +315,22 @@ namespace ICSharpCode.Core
 			         Char.IsDigit(ch));
 		}
 		
+		/// <summary>
+		/// Checks that a single directory name (not the full path) is valid.
+		/// </summary>
+		public static bool IsValidDirectoryName(string name)
+		{
+			if (!IsValidFileName(name)) {
+				return false;
+			}
+			if (name.IndexOfAny(new char[]{Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar}) >= 0) {
+				return false;
+			}
+			if (name.Trim(' ').Length == 0) {
+				return false;
+			}
+			return true;
+		}
 		
 		public static bool TestFileExists(string filename)
 		{
diff --git a/src/Main/Core/Test/ICSharpCode.Core.Tests.csproj b/src/Main/Core/Test/ICSharpCode.Core.Tests.csproj
index 02cc4cbed9..450dae3f57 100644
--- a/src/Main/Core/Test/ICSharpCode.Core.Tests.csproj
+++ b/src/Main/Core/Test/ICSharpCode.Core.Tests.csproj
@@ -48,6 +48,7 @@
     <Compile Include="StringParserTests.cs" />
     <Compile Include="AddInTreeTests\AddInTreeLoadingTests.cs" />
     <Compile Include="AddInTreeTests\ExtPathTests.cs" />
+    <Compile Include="InvalidDirectoryNameTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Project\ICSharpCode.Core.csproj">
diff --git a/src/Main/Core/Test/InvalidDirectoryNameTests.cs b/src/Main/Core/Test/InvalidDirectoryNameTests.cs
new file mode 100644
index 0000000000..7855adc944
--- /dev/null
+++ b/src/Main/Core/Test/InvalidDirectoryNameTests.cs
@@ -0,0 +1,40 @@
+// <file>
+//     <copyright see="prj:///doc/copyright.txt"/>
+//     <license see="prj:///doc/license.txt"/>
+//     <owner name="Matthew Ward" email="mrward@users.sourceforge.net"/>
+//     <version>$Revision$</version>
+// </file>
+
+using NUnit.Framework;
+using System;
+
+namespace ICSharpCode.Core.Tests
+{
+	[TestFixture]
+	public class InvalidDirectoryNameTests
+	{
+		[Test]
+		public void ContainsBackslash()
+		{
+			Assert.IsFalse(FileUtility.IsValidDirectoryName(@"project\test"));
+		}
+		
+		[Test]
+		public void ContainsForwardSlash()
+		{
+			Assert.IsFalse(FileUtility.IsValidDirectoryName(@"project/test"));
+		}
+		
+		[Test]
+		public void IsPRN()
+		{
+			Assert.IsFalse(FileUtility.IsValidDirectoryName("PRN"));
+		}
+		
+		[Test]
+		public void IsEmptySpace()
+		{
+			Assert.IsFalse(FileUtility.IsValidDirectoryName(" "));
+		}
+	}
+}