diff --git a/src/Main/Base/Project/Src/Gui/Dialogs/OptionPanels/ExternalToolPanel.cs b/src/Main/Base/Project/Src/Gui/Dialogs/OptionPanels/ExternalToolPanel.cs
index 42d10b0f9b..2c02635a9c 100644
--- a/src/Main/Base/Project/Src/Gui/Dialogs/OptionPanels/ExternalToolPanel.cs
+++ b/src/Main/Base/Project/Src/Gui/Dialogs/OptionPanels/ExternalToolPanel.cs
@@ -149,11 +149,11 @@ namespace ICSharpCode.SharpDevelop.Gui.OptionPanels
 		{
 			List<ExternalTool> newlist = new List<ExternalTool>();
 			foreach (ExternalTool tool in ((ListBox)ControlDictionary["toolListBox"]).Items) {
-				if (!FileUtility.IsValidPath(tool.Command)) {
+				if (!FileUtility.IsValidPath(StringParser.Parse(tool.Command))) {
 					MessageService.ShowError(String.Format("The command of tool \"{0}\" is invalid.", tool.MenuCommand));
 					return false;
 				}
-				if ((tool.InitialDirectory != "") && (!FileUtility.IsValidPath(tool.InitialDirectory))) {
+				if ((tool.InitialDirectory != String.Empty) && (!FileUtility.IsValidPath(tool.InitialDirectory))) {
 					MessageService.ShowError(String.Format("The working directory of tool \"{0}\" is invalid.", tool.MenuCommand));
 					return false;
 				}