diff --git a/OpenRA.Game/Exts.cs b/OpenRA.Game/Exts.cs
index 64fad44cc3..07021dc184 100644
--- a/OpenRA.Game/Exts.cs
+++ b/OpenRA.Game/Exts.cs
@@ -87,6 +87,29 @@ namespace OpenRA
 			return r.Contains(p.ToPointF());
 		}
 
+		static int WindingDirectionTest(int2 v0, int2 v1, int2 p)
+		{
+			return (v1.X - v0.X) * (p.Y - v0.Y) - (p.X - v0.X) * (v1.Y - v0.Y);
+		}
+
+		public static bool PolygonContains(this int2[] polygon, int2 p)
+		{
+			var windingNumber = 0;
+
+			for (var i = 0; i < polygon.Length; i++)
+			{
+				var tv = polygon[i];
+				var nv = polygon[(i + 1) % polygon.Length];
+
+				if (tv.Y <= p.Y && nv.Y > p.Y && WindingDirectionTest(tv, nv, p) > 0)
+					windingNumber++;
+				else if (tv.Y > p.Y && nv.Y <= p.Y && WindingDirectionTest(tv, nv, p) < 0)
+					windingNumber--;
+			}
+
+			return windingNumber != 0;
+		}
+
 		public static bool HasModifier(this Modifiers k, Modifiers mod)
 		{
 			return (k & mod) == mod;
diff --git a/OpenRA.Game/Graphics/Viewport.cs b/OpenRA.Game/Graphics/Viewport.cs
index c09fc5bb94..03c5e87f05 100644
--- a/OpenRA.Game/Graphics/Viewport.cs
+++ b/OpenRA.Game/Graphics/Viewport.cs
@@ -105,9 +105,66 @@ namespace OpenRA.Graphics
 
 		public CPos ViewToWorld(int2 view)
 		{
+			var world = worldRenderer.Viewport.ViewToWorldPx(view);
+			var map = worldRenderer.World.Map;
+			var ts = Game.ModData.Manifest.TileSize;
+			var candidates = CandidateMouseoverCells(world);
+			var tileSet = worldRenderer.World.TileSet;
+
+			foreach (var uv in candidates)
+			{
+				// Coarse filter to nearby cells
+				var p = map.CenterOfCell(uv.ToCPos(map.TileShape));
+				var s = worldRenderer.ScreenPxPosition(p);
+				if (Math.Abs(s.X - world.X) <= ts.Width && Math.Abs(s.Y - world.Y) <= ts.Height)
+				{
+					var tile = map.MapTiles.Value[uv];
+					var ti = tileSet.GetTileInfo(tile);
+					var ramp = ti != null ? ti.RampType : 0;
+
+					var corners = map.CellCorners[ramp];
+					var pos = map.CenterOfCell(uv.ToCPos(map));
+					var screen = corners.Select(c => worldRenderer.ScreenPxPosition(pos + c)).ToArray();
+
+					if (screen.PolygonContains(world))
+						return uv.ToCPos(map);
+				}
+			}
+
+			// Mouse is not directly over a cell (perhaps on a cliff)
+			// Try and find the closest cell
+			if (candidates.Any())
+			{
+				return candidates.OrderBy(uv =>
+				{
+					var p = map.CenterOfCell(uv.ToCPos(map.TileShape));
+					var s = worldRenderer.ScreenPxPosition(p);
+					var dx = Math.Abs(s.X - world.X);
+					var dy = Math.Abs(s.Y - world.Y);
+
+					return dx * dx + dy * dy;
+				}).First().ToCPos(map);
+			}
+
+			// Something is very wrong, but lets return something that isn't completely bogus and hope the caller can recover
 			return worldRenderer.World.Map.CellContaining(worldRenderer.Position(ViewToWorldPx(view)));
 		}
 
+		/// <summary> Returns an unfiltered list of all cells that could potentially contain the mouse cursor</summary>
+		IEnumerable<MPos> CandidateMouseoverCells(int2 world)
+		{
+			var map = worldRenderer.World.Map;
+			var minPos = worldRenderer.Position(world);
+
+			// Find all the cells that could potentially have been clicked
+			var a = map.CellContaining(minPos - new WVec(1024, 0, 0)).ToMPos(map.TileShape);
+			var b = map.CellContaining(minPos + new WVec(512, 512 * maxGroundHeight, 0)).ToMPos(map.TileShape);
+
+			for (var v = b.V; v >= a.V; v--)
+				for (var u = b.U; u >= a.U; u--)
+					yield return new MPos(u, v);
+		}
+
 		public int2 ViewToWorldPx(int2 view) { return (1f / Zoom * view.ToFloat2()).ToInt2() + TopLeft; }
 		public int2 WorldToViewPx(int2 world) { return (Zoom * (world - TopLeft).ToFloat2()).ToInt2(); }
 
diff --git a/OpenRA.Mods.Common/Traits/World/TerrainGeometryOverlay.cs b/OpenRA.Mods.Common/Traits/World/TerrainGeometryOverlay.cs
index 5a7b5eff86..6e0ab280db 100644
--- a/OpenRA.Mods.Common/Traits/World/TerrainGeometryOverlay.cs
+++ b/OpenRA.Mods.Common/Traits/World/TerrainGeometryOverlay.cs
@@ -37,19 +37,21 @@ namespace OpenRA.Mods.Common.Traits
 			if (devMode.Value == null || !devMode.Value.ShowTerrainGeometry)
 				return;
 
+			var map = wr.World.Map;
+			var tileSet = wr.World.TileSet;
 			var lr = Game.Renderer.WorldLineRenderer;
 			var colors = wr.World.TileSet.HeightDebugColors;
 
 			foreach (var uv in wr.Viewport.VisibleCells.MapCoords)
 			{
-				var height = (int)wr.World.Map.MapHeight.Value[uv];
-				var tile = wr.World.Map.MapTiles.Value[uv];
-				var ti = wr.World.TileSet.GetTileInfo(tile);
+				var height = (int)map.MapHeight.Value[uv];
+				var tile = map.MapTiles.Value[uv];
+				var ti = tileSet.GetTileInfo(tile);
 				var ramp = ti != null ? ti.RampType : 0;
 
-				var corners = wr.World.Map.CellCorners[ramp];
+				var corners = map.CellCorners[ramp];
 				var color = corners.Select(c => colors[height + c.Z / 512]).ToArray();
-				var pos = wr.World.Map.CenterOfCell(uv.ToCPos(wr.World.Map));
+				var pos = map.CenterOfCell(uv.ToCPos(map));
 				var screen = corners.Select(c => wr.ScreenPxPosition(pos + c).ToFloat2()).ToArray();
 
 				for (var i = 0; i < 4; i++)