diff --git a/compat/game21/custom_walls.lua b/compat/game21/custom_walls.lua
index 8c2c4c0..db581cf 100644
--- a/compat/game21/custom_walls.lua
+++ b/compat/game21/custom_walls.lua
@@ -25,7 +25,7 @@ local function create_cw(deadly, collision)
     cw.collision = collision
     cw.deadly = deadly
     cw.killing_side = 0
-    return handle
+    return handle - 1
 end
 cws.cw_create = function()
     return create_cw(false, true)
@@ -36,28 +36,30 @@ end
 cws.cw_createNoCollision = function()
     return create_cw(false, false)
 end
-local function is_valid_handle(handle)
+local function process_handle(handle)
+    handle = handle + 1
     if custom_walls[handle] == nil then
         error("Trying to access invalid cw handle: " .. handle)
     end
+    return handle
 end
 cws.cw_destroy = function(handle)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].visible = false
     free_handles[#free_handles + 1] = handle
 end
 cws.cw_setVertexPos = function(handle, vertex, x, y)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].vertices[vertex * 2 + 1] = x
     custom_walls[handle].vertices[vertex * 2 + 2] = y
 end
 cws.cw_moveVertexPos = function(handle, vertex, offset_x, offset_y)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].vertices[vertex * 2 + 1] = custom_walls[handle].vertices[vertex * 2 + 1] + offset_x
     custom_walls[handle].vertices[vertex * 2 + 2] = custom_walls[handle].vertices[vertex * 2 + 2] + offset_y
 end
 cws.cw_moveVertexPos4Same = function(handle, offset_x, offset_y)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].vertices[1] = custom_walls[handle].vertices[1] + offset_x
     custom_walls[handle].vertices[2] = custom_walls[handle].vertices[2] + offset_y
     custom_walls[handle].vertices[3] = custom_walls[handle].vertices[3] + offset_x
@@ -68,14 +70,14 @@ cws.cw_moveVertexPos4Same = function(handle, offset_x, offset_y)
     custom_walls[handle].vertices[8] = custom_walls[handle].vertices[8] + offset_y
 end
 cws.cw_setVertexColor = function(handle, vertex, r, g, b, a)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].colors[vertex * 4 + 1] = r
     custom_walls[handle].colors[vertex * 4 + 2] = g
     custom_walls[handle].colors[vertex * 4 + 3] = b
     custom_walls[handle].colors[vertex * 4 + 4] = a
 end
 cws.cw_setVertexPos4 = function(handle, x0, y0, x1, y1, x2, y2, x3, y3)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].vertices[1] = x0
     custom_walls[handle].vertices[2] = y0
     custom_walls[handle].vertices[3] = x1
@@ -86,7 +88,7 @@ cws.cw_setVertexPos4 = function(handle, x0, y0, x1, y1, x2, y2, x3, y3)
     custom_walls[handle].vertices[8] = y3
 end
 cws.cw_setVertexColor4 = function(handle, r0, g0, b0, a0, r1, g1, b1, a1, r2, g2, b2, a2, r3, g3, b3, a3)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].colors[1] = r0
     custom_walls[handle].colors[2] = g0
     custom_walls[handle].colors[3] = b0
@@ -105,7 +107,7 @@ cws.cw_setVertexColor4 = function(handle, r0, g0, b0, a0, r1, g1, b1, a1, r2, g2
     custom_walls[handle].colors[16] = a3
 end
 cws.cw_setVertexColor4Same = function(handle, r, g, b, a)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     for i = 0, 3 do
         custom_walls[handle].colors[i * 4 + 1] = r
         custom_walls[handle].colors[i * 4 + 2] = g
@@ -114,35 +116,35 @@ cws.cw_setVertexColor4Same = function(handle, r, g, b, a)
     end
 end
 cws.cw_setCollision = function(handle, collision)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].collision = collision
 end
 cws.cw_setDeadly = function(handle, deadly)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].deadly = deadly
 end
 cws.cw_setKillingSide = function(handle, side)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     custom_walls[handle].killing_side = side
 end
 cws.cw_getCollision = function(handle)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     return custom_walls[handle].collision
 end
 cws.cw_getDeadly = function(handle)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     return custom_walls[handle].deadly
 end
 cws.cw_getKillingSide = function(handle)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     return custom_walls[handle].killing_side
 end
 cws.cw_getVertexPos = function(handle, vertex)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     return custom_walls[handle].vertices[vertex * 2 + 1], custom_walls[handle].vertices[vertex * 2 + 2]
 end
 cws.cw_getVertexPos4 = function(handle)
-    is_valid_handle(handle)
+    handle = process_handle(handle)
     return custom_walls[handle].vertices[1],
         custom_walls[handle].vertices[2],
         custom_walls[handle].vertices[3],