diff --git a/OpenRa.Game/Graphics/TerrainRenderer.cs b/OpenRa.Game/Graphics/TerrainRenderer.cs
index 212dfe423f..d0adbf6ebf 100644
--- a/OpenRa.Game/Graphics/TerrainRenderer.cs
+++ b/OpenRa.Game/Graphics/TerrainRenderer.cs
@@ -55,7 +55,7 @@ namespace OpenRa.Graphics
 			int indicesPerRow = map.Width * 6;
 			int verticesPerRow = map.Width * 4;
 
-			int visibleRows = (int)(viewport.Width / 24.0f + 2);
+			int visibleRows = (int)(viewport.Height / 24.0f + 2);
 
 			int firstRow = (int)((viewport.Location.Y) / 24.0f - map.YOffset);
 			int lastRow = firstRow + visibleRows;