diff --git a/main.lua b/main.lua
index a334199..add137f 100644
--- a/main.lua
+++ b/main.lua
@@ -142,7 +142,7 @@ local nn_x, nn_tx, nn_ty, nn_y, nn_z
 local function make_network(input_size)
     nn_x = nn.Input({input_size})
     nn_tx = nn.Input({gcfg.tile_count})
-    nn_ty = nn_tx:feed(nn.Embed(256, 2))
+    nn_ty = nn_tx:feed(nn.Embed(#game.valid_tiles, 2))
     nn_y = nn.Merge()
     nn_x:feed(nn_y)
     nn_ty:feed(nn_y)
diff --git a/smb.lua b/smb.lua
index cb073b2..dbda609 100644
--- a/smb.lua
+++ b/smb.lua
@@ -11,6 +11,22 @@ local R = memory.readbyteunsigned
 local W = memory.writebyte
 local function S(addr) return util.signbyte(R(addr)) end
 
+local valid_tiles = {
+    0x00, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
+    0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E,
+    0x1F, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26,
+    0x51, 0x52, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59,
+    0x5A, 0x5B, 0x5C, 0x5D, 0x5E, 0x5F, 0x60, 0x61,
+    0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
+    0x6B, 0x6C, 0x89, 0xC0, 0xC1, 0xC2, 0xC3, 0xC4,
+    0xC5
+}
+
+local tile_lut = {}
+for i, v in ipairs(valid_tiles) do
+    tile_lut[v] = i - 1
+end
+
 local rotation_offsets = { -- FIXME: not all of these are pixel-perfect.
     0, -40, -- 0x00
     6, -38,
@@ -91,7 +107,7 @@ local function mark_sprite(x, y, t)
 end
 
 local function mark_tile(x, y, t)
-    tile_input[#tile_input+1] = t
+    tile_input[#tile_input+1] = tile_lut[t]
     if t == 0 then return end
     if overlay then
         gui.box(x-8, y-8, x+8, y+8)
@@ -270,6 +286,8 @@ W=W,
 S=S,
 overlay=overlay,
 
+valid_tiles=valid_tiles,
+
 sprite_input=sprite_input,
 tile_input=tile_input,
 extra_input=extra_input,