diff --git a/Source/Core/IO/WAD.cs b/Source/Core/IO/WAD.cs
index 540a3e5..ac5907d 100644
--- a/Source/Core/IO/WAD.cs
+++ b/Source/Core/IO/WAD.cs
@@ -32,6 +32,7 @@ namespace CodeImp.DoomBuilder.IO
 		// WAD types
 		public const string TYPE_IWAD = "IWAD";
 		public const string TYPE_PWAD = "PWAD";
+        public const string TYPE_ZWAD = "ZWAD";
 		
 		// Encoder
 		public static readonly Encoding ENCODING = Encoding.ASCII;
@@ -194,6 +195,9 @@ namespace CodeImp.DoomBuilder.IO
 
 			// Read WAD type
 			type = ENCODING.GetString(reader.ReadBytes(4));
+
+            if (type == TYPE_ZWAD)
+                throw new IOException("Sorry, can't open ZWADs. Please decompress first.");
 			
 			// Number of lumps
 			numlumps = reader.ReadInt32();
diff --git a/Source/Core/Windows/ChangeMapForm.cs b/Source/Core/Windows/ChangeMapForm.cs
index 192b13f..522c4b6 100644
--- a/Source/Core/Windows/ChangeMapForm.cs
+++ b/Source/Core/Windows/ChangeMapForm.cs
@@ -45,11 +45,11 @@ namespace CodeImp.DoomBuilder.Windows
 				// Open the WAD file
 				wadfile = new WAD(filepathname, true);
 			}
-			catch(Exception)
+			catch(Exception e)
 			{
-				// Unable to open WAD file (or its config)
-				MessageBox.Show(this, "Could not open the WAD file for reading. Please make sure the file you selected is valid and is not in use by any other application.", Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
-				this.DialogResult = DialogResult.Cancel;
+                // Unable to open WAD file (or its config)
+                MessageBox.Show(this, "Could not open the WAD file for reading.\n" + e.GetType().Name + ": " + e.Message + "\nPlease make sure the file you selected is valid and is not in use by any other application.", Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
+                this.DialogResult = DialogResult.Cancel;
 				this.Close();
 				return;
 			}
diff --git a/Source/Core/Windows/OpenMapOptionsForm.cs b/Source/Core/Windows/OpenMapOptionsForm.cs
index 7960737..cfcfe6f 100644
--- a/Source/Core/Windows/OpenMapOptionsForm.cs
+++ b/Source/Core/Windows/OpenMapOptionsForm.cs
@@ -90,10 +90,10 @@ namespace CodeImp.DoomBuilder.Windows
 				// Open the WAD file
 				wadfile = new WAD(filepathname, true);
 			}
-			catch(Exception)
+			catch(Exception e)
 			{
-				// Unable to open WAD file (or its config)
-				MessageBox.Show(this, "Could not open the WAD file for reading. Please make sure the file you selected is valid and is not in use by any other application.", Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
+                // Unable to open WAD file (or its config)
+                MessageBox.Show(this, "Could not open the WAD file for reading.\n" + e.GetType().Name + ": " + e.Message + "\nPlease make sure the file you selected is valid and is not in use by any other application.", Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
 				if(wadfile != null) wadfile.Dispose();
 				this.DialogResult = DialogResult.Cancel;
 				this.Close();