diff --git a/data/lua/cave_map_generator.lua b/data/lua/cave_map_generator.lua
index 962d1df4fef..31ce5e70316 100644
--- a/data/lua/cave_map_generator.lua
+++ b/data/lua/cave_map_generator.lua
@@ -122,7 +122,7 @@ function callbacks.generate_map(params)
 			local width = math.max(v.data.width or 1, 1)
 			local jagged = v.data.jagged or 0
 			local calc = function(x, y)
-				if x == 0 or x == params.map_width or y == 0 or y == params.map_height then
+				if x == 0 or x == params.map_width - 1 or y == 0 or y == params.map_height - 1 then
 					-- Map borders are impassable
 					return math.huge
 				end