Index: source/simulation2/components/CCmpRangeManager.cpp
===================================================================
--- source/simulation2/components/CCmpRangeManager.cpp
+++ source/simulation2/components/CCmpRangeManager.cpp
@@ -2179,6 +2179,9 @@
 		// (so that we never render the sharp edge of the map)
 		i32 j0 = ((pos.Y - visionRange)/(int)TERRAIN_TILE_SIZE).ToInt_RoundToInfinity();
 		i32 j1 = ((pos.Y + visionRange)/(int)TERRAIN_TILE_SIZE).ToInt_RoundToNegInfinity();
+		if (j1 <= j0)
+			// Make sure that we highlight at least one tile.
+			j1 = j0 + 1;
 		i32 j0clamp = std::max(j0, 1);
 		i32 j1clamp = std::min(j1, m_TerrainVerticesPerSide-2);
 
@@ -2193,6 +2196,7 @@
 		i32 xceil = (x + entity_pos_t::Epsilon()).ToInt_RoundToInfinity();
 
 		// Initialise the strip (i0, i1) to a rough guess
+		// Here i1 > i0;
 		i32 i0 = xfloor;
 		i32 i1 = xceil;
 
@@ -2202,16 +2206,17 @@
 			// the circle's radius (i.e. require dy^2 + dx^2 <= r^2).
 			// When moving the points inwards, clamp them to xceil+1 or xfloor-1
 			// so they don't accidentally shoot off in the wrong direction forever.
+			// Also make sure that we have at least one tile difference between i0 and i1
 
 			entity_pos_t dy = entity_pos_t::FromInt(j) - y;
 			entity_pos_t dy2 = dy.Square();
 			while (dy2 + (entity_pos_t::FromInt(i0-1) - x).Square() <= r2)
 				--i0;
-			while (i0 < xceil && dy2 + (entity_pos_t::FromInt(i0) - x).Square() > r2)
+			while (i0 < xceil && i0 < i1 - 1 && dy2 + (entity_pos_t::FromInt(i0) - x).Square() > r2)
 				++i0;
 			while (dy2 + (entity_pos_t::FromInt(i1+1) - x).Square() <= r2)
 				++i1;
-			while (i1 > xfloor && dy2 + (entity_pos_t::FromInt(i1) - x).Square() > r2)
+			while (i1 > xfloor && i1 - 1 > i0 && dy2 + (entity_pos_t::FromInt(i1) - x).Square() > r2)
 				--i1;
 
 #if DEBUG_RANGE_MANAGER_BOUNDS