diff --git a/static/script.js b/static/script.js
index 9dfaab4f..7a3062ac 100644
--- a/static/script.js
+++ b/static/script.js
@@ -3607,13 +3607,18 @@ const DUNGEON_DISPLAY_COLORS = {
   stairs:      { r: 180, g: 160, b: 80  },  // yellowish stairs
 };
 
-// Process a tile image: make white transparent, remap UB colors
+// Process a tile image: flip horizontally (UB tiles authored for mirrored-X),
+// make white transparent, remap UB colors
 function processTileImage(img) {
   const c = document.createElement('canvas');
   c.width = 10;
   c.height = 10;
   const ctx = c.getContext('2d');
+  // Flip horizontally: tiles were designed for UB's mirrored-X coordinate system
+  ctx.translate(10, 0);
+  ctx.scale(-1, 1);
   ctx.drawImage(img, 0, 0, 10, 10);
+  ctx.setTransform(1, 0, 0, 1, 0, 0);
   const imageData = ctx.getImageData(0, 0, 10, 10);
   const d = imageData.data;
 
@@ -3857,13 +3862,14 @@ function updateRadarWindow(msg) {
     const cellSize = 10 * scale; // each cell is 10 game units
     const hasTiles = dungeonTileCanvases && Object.keys(dungeonTileCanvases).length > 0;
 
-    // Normalize rotation value to radians (same as UB's DungeonCell.cs)
-    // Raw value is quaternion W component: 1→180°, ~0.707→-90°, ~-0.707→90°, 0→0°
+    // Normalize rotation value to radians (from UB's DungeonCell.cs)
+    // Negated because tile images are horizontally flipped to compensate
+    // for UB's mirrored-X authoring space
     function cellRotation(rot) {
-      if (Math.abs(rot - 1) < 0.01) return Math.PI;
+      if (Math.abs(rot - 1) < 0.01) return Math.PI;   // 180° = -180°, same
       if (Math.abs(rot + 1) < 0.01) return Math.PI;
-      if (rot < -0.70 && rot > -0.8) return Math.PI / 2;
-      if (rot > 0.70 && rot < 0.8) return -Math.PI / 2;
+      if (rot < -0.70 && rot > -0.8) return -Math.PI / 2;  // negated
+      if (rot > 0.70 && rot < 0.8) return Math.PI / 2;     // negated
       return 0;
     }