diff --git a/src/App.TileMapBG0.s b/src/App.TileMapBG0.s
index ab7c26d..f7f4e69 100644
--- a/src/App.TileMapBG0.s
+++ b/src/App.TileMapBG0.s
@@ -386,7 +386,7 @@ App_TileMapBG0
         dw 41,41,41,41,41,41,41,41,41,41,41,41,41,41,41,41
         dw 41,41,56,21,21,21,21,59,41,41,41,41,41,41,41,41
         dw 41,41,41,41,41,41,41,41,41,41,41,41,41,41,41,41
-        dw 41,41,57,2147483705,41,41,41,41,41,41,41,41,41,41,41,41
+        dw 41,41,57,569,41,41,41,41,41,41,41,41,41,41,41,41
         dw 41,41,41,41,41,41,41,41,15,16,17,18,41,41,41,41
         dw 41,41,41,41,41,41,41,41,41,41,41,41,19,20,21,22
         dw 41,41,41,41,41,41,41,41,41,41,41,41,19,20,21,22
@@ -402,7 +402,7 @@ App_TileMapBG0
         dw 41,41,41,41,41,41,41,41,41,41,41,41,41,41,41,41
         dw 41,56,21,62,21,21,62,21,59,41,41,41,41,41,41,41
         dw 41,41,41,41,41,41,41,41,42,43,42,43,42,43,41,41
-        dw 41,56,21,62,2147483704,41,41,41,41,41,41,41,41,41,41,41
+        dw 41,56,21,62,568,41,41,41,41,41,41,41,41,41,41,41
         dw 42,43,41,41,41,41,41,41,19,20,21,22,41,41,41,41
         dw 41,41,41,41,41,41,41,41,41,41,41,41,19,20,21,22
         dw 41,41,41,41,42,43,42,43,41,41,41,41,19,20,21,22
@@ -418,7 +418,7 @@ App_TileMapBG0
         dw 41,41,41,41,41,41,41,41,41,41,41,41,41,41,41,41
         dw 56,21,21,21,21,21,21,21,21,59,41,41,41,41,41,41
         dw 41,41,41,41,41,41,41,44,45,45,45,45,45,45,46,41
-        dw 56,21,21,21,21,2147483704,41,41,41,41,41,41,41,41,41,44
+        dw 56,21,21,21,21,568,41,41,41,41,41,41,41,41,41,44
         dw 45,45,46,41,41,41,41,41,19,20,21,22,41,41,41,41
         dw 41,41,41,41,41,41,41,41,41,41,41,41,19,20,21,22
         dw 41,41,41,44,45,45,45,45,46,41,41,41,19,20,21,22
diff --git a/tools/tiled2iigs.js b/tools/tiled2iigs.js
index 4a2b44f..f7bdadb 100644
--- a/tools/tiled2iigs.js
+++ b/tools/tiled2iigs.js
@@ -219,7 +219,7 @@ function emitLayerData(sb, layer) {
     const chunks = [];
     const tileIDs = layer.data;
     for (let i = 0; i < tileIDs.length; i += N) {
-        chunks.push(tileIDs.slice(i, i + N))
+        chunks.push(tileIDs.slice(i, i + N).map(t => convertTileID(t)))
     }
     // Tiled starts numbering its tiles at 1. This is OK since Tile 0 is reserved in
     // GTE, also
@@ -228,4 +228,29 @@ function emitLayerData(sb, layer) {
     }
 
     return sb;
+}
+
+/**
+ * Map the bit flags used in Tiled to compatible values in GTE
+ */
+function convertTileID(tileId) {
+    const GTE_VFLIP_BIT = 0x0400;
+    const GTE_HFLIP_BIT = 0x0200;
+    const TILED_VFLIP_BIT = 0x40000000;
+    const TILED_HFLIP_BIT = 0x80000000;
+    const TILED_DFLIP_BIT = 0x20000000;
+
+    // We don't support the flipped diagonally flag or tile values greater than 511
+    if ((tileId & TILED_DFLIP_BIT) !== 0) {
+        throw new Error('Diagonally flipped bits are not supported: tileId =  ' + tileId.toString(16));
+    }
+
+    const hflip = (tileId & TILED_HFLIP_BIT) !== 0;
+    const vflip = (tileId & TILED_VFLIP_BIT) !== 0;
+
+    if ((tileId & 0x1FFFFFFF) > 511) {
+        throw new Error('A maximum of 511 tiles are supported');
+    }
+
+    return (tileId & 0x1FFFFFFF) + (hflip ? GTE_HFLIP_BIT : 0) + (vflip ? GTE_VFLIP_BIT : 0);
 }
\ No newline at end of file