diff --git a/ChangeLog b/ChangeLog
index 265fcae11..f17b42ef4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2004-04-12  Mike Kestner  <mkestner@ximian.com>
+
+	* gnome/Program.custom : add ArgumentException for app_id containing
+	spaces.  [fixes #56594]
+
 2004-04-12  Mike Kestner  <mkestner@ximian.com>
 
 	[Rework of a patch from Ben Maurer to turn GLib.Value
diff --git a/gnome/Program.custom b/gnome/Program.custom
index 3a57fcb9e..55a9d7aa6 100644
--- a/gnome/Program.custom
+++ b/gnome/Program.custom
@@ -23,6 +23,9 @@ gtksharp_gnome_program_init (string app_id, string app_version, ref ModuleInfo m
 
 public Program (string app_id, string app_version, ModuleInfo module, string[] argv, params object[] props) : base (IntPtr.Zero)
 {
+	if (app_id.IndexOf (" ") > 0)
+		throw new ArgumentException ("app_id argument can't contain spaces.");
+
 	int nargs = props.Length / 2;
 	PropertyArg[] args = new PropertyArg[nargs];
 	GLib.Value[] vals = new GLib.Value[nargs];