diff --git a/OpenRA.Game/Exts.cs b/OpenRA.Game/Exts.cs
index b5e3a6c9de..6acf22c314 100644
--- a/OpenRA.Game/Exts.cs
+++ b/OpenRA.Game/Exts.cs
@@ -11,6 +11,7 @@
 using System;
 using System.Collections.Generic;
 using System.Drawing;
+using System.Drawing.Imaging;
 using System.Globalization;
 using System.Linq;
 using System.Reflection;
@@ -434,6 +435,25 @@ namespace OpenRA
 
 		public static Rectangle Bounds(this Bitmap b) { return new Rectangle(0, 0, b.Width, b.Height); }
 
+		public static Bitmap CloneWith32bbpArgbPixelFormat(this Bitmap original)
+		{
+			// Note: We would use original.Clone(original.Bounds(), PixelFormat.Format32bppArgb)
+			// but this doesn't work on mono.
+			var clone = new Bitmap(original.Width, original.Height, PixelFormat.Format32bppArgb);
+			try
+			{
+				using (var g = System.Drawing.Graphics.FromImage(clone))
+					g.DrawImage(original, original.Bounds());
+			}
+			catch (Exception)
+			{
+				clone.Dispose();
+				throw;
+			}
+
+			return clone;
+		}
+
 		public static int ToBits(this IEnumerable<bool> bits)
 		{
 			var i = 0;
diff --git a/OpenRA.Game/Graphics/Util.cs b/OpenRA.Game/Graphics/Util.cs
index d0b05396f0..9851fcff52 100644
--- a/OpenRA.Game/Graphics/Util.cs
+++ b/OpenRA.Game/Graphics/Util.cs
@@ -64,6 +64,9 @@ namespace OpenRA.Graphics
 
 		public static void FastCopyIntoSprite(Sprite dest, Bitmap src)
 		{
+			if (src.PixelFormat != PixelFormat.Format32bppArgb)
+				throw new ArgumentException("src must have a PixelFormat of Format32bppArgb", "src");
+
 			var data = dest.Sheet.GetData();
 			var dataStride = dest.Sheet.Size.Width * 4;
 			var x = dest.Bounds.Left * 4;
@@ -72,7 +75,7 @@ namespace OpenRA.Graphics
 			var height = dest.Bounds.Height;
 
 			var bd = src.LockBits(src.Bounds(),
-				ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
+				ImageLockMode.ReadWrite, src.PixelFormat);
 			for (var row = 0; row < height; row++)
 				Marshal.Copy(IntPtr.Add(bd.Scan0, row * bd.Stride), data, (y + row) * dataStride + x, width);
 			src.UnlockBits(bd);
diff --git a/OpenRA.Game/Map/Map.cs b/OpenRA.Game/Map/Map.cs
index 782c7fdbf8..ffbcf494ba 100644
--- a/OpenRA.Game/Map/Map.cs
+++ b/OpenRA.Game/Map/Map.cs
@@ -12,6 +12,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Drawing;
+using System.Drawing.Imaging;
 using System.IO;
 using System.Linq;
 using System.Security.Cryptography;
@@ -391,8 +392,16 @@ namespace OpenRA
 			DefaultSubCell = (SubCell)Game.ModData.Manifest.SubCellDefaultIndex;
 
 			if (Container.Exists("map.png"))
+			{
 				using (var dataStream = Container.GetContent("map.png"))
 					CustomPreview = new Bitmap(dataStream);
+				if (CustomPreview.PixelFormat != PixelFormat.Format32bppArgb)
+				{
+					var original = CustomPreview;
+					CustomPreview = original.CloneWith32bbpArgbPixelFormat();
+					original.Dispose();
+				}
+			}
 
 			PostInit();
 
diff --git a/OpenRA.Game/Map/MapCache.cs b/OpenRA.Game/Map/MapCache.cs
index 0303c32795..44bc4a9d9c 100644
--- a/OpenRA.Game/Map/MapCache.cs
+++ b/OpenRA.Game/Map/MapCache.cs
@@ -11,6 +11,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Drawing.Imaging;
 using System.IO;
 using System.Linq;
 using System.Net;
@@ -174,6 +175,11 @@ namespace OpenRA
 						createdPreview = true;
 						bitmap = Minimap.RenderMapPreview(modData.DefaultRules.TileSets[p.Map.Tileset], p.Map, modData.DefaultRules, true);
 					}
+					else if (bitmap.PixelFormat != PixelFormat.Format32bppArgb)
+					{
+						Log.Write("debug", "Discarding invalid map preview for {0}", p.Uid);
+						continue;
+					}
 
 					// Note: this is not generally thread-safe, but it works here because:
 					//   (a) This worker is the only thread writing to this sheet
diff --git a/OpenRA.Game/Map/MapPreview.cs b/OpenRA.Game/Map/MapPreview.cs
index fb843d1eaa..2b85004f38 100644
--- a/OpenRA.Game/Map/MapPreview.cs
+++ b/OpenRA.Game/Map/MapPreview.cs
@@ -13,6 +13,7 @@ using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 using System.Drawing;
+using System.Drawing.Imaging;
 using System.IO;
 using System.Linq;
 using System.Net;
@@ -155,6 +156,12 @@ namespace OpenRA
 						SpawnPoints = spawns;
 
 						CustomPreview = new Bitmap(new MemoryStream(Convert.FromBase64String(r.minimap)));
+						if (CustomPreview.PixelFormat != PixelFormat.Format32bppArgb)
+						{
+							var original = CustomPreview;
+							CustomPreview = original.CloneWith32bbpArgbPixelFormat();
+							original.Dispose();
+						}
 					}
 					catch (Exception) { }