diff --git a/scripts/lib/StarterThemer.js b/scripts/lib/StarterThemer.js
index 20f93d5dd..50293389f 100644
--- a/scripts/lib/StarterThemer.js
+++ b/scripts/lib/StarterThemer.js
@@ -836,17 +836,27 @@ const applyThemeToStarter = (
                 instance.y -
                 (placeholderFrame.originPoint.y * instance.height) /
                   placeholderImage.height;
-              const width = firstThemed.slot.width * scale;
-              const height = firstThemed.slot.height * scale;
+              // Art wider than the instance is drawn at half the scale, so
+              // that it does not cover what is next to the instance.
+              const isHalved =
+                scale % 2 === 0 &&
+                firstThemed.slot.width * scale > instance.width;
+              const instanceScale = isHalved ? scale / 2 : scale;
+              const width = firstThemed.slot.width * instanceScale;
+              const height = firstThemed.slot.height * instanceScale;
               instance.x =
-                left + (instance.width - width) / 2 + themedOrigin.x * scale;
+                left +
+                (instance.width - width) / 2 +
+                themedOrigin.x * instanceScale;
               instance.y =
                 top +
                 (anchor === 'bottom'
                   ? instance.height - height
                   : (instance.height - height) / 2) +
-                themedOrigin.y * scale;
-              instance.customSize = false;
+                themedOrigin.y * instanceScale;
+              instance.customSize = isHalved;
+              instance.width = width;
+              instance.height = height;
             }
           );
           if (usedSlotIds.length === 1 && firstThemed.slot.assetStoreId) {
diff --git a/scripts/lib/__tests__/StarterThemer.spec.js b/scripts/lib/__tests__/StarterThemer.spec.js
index b0189aa0d..247cc826e 100644
--- a/scripts/lib/__tests__/StarterThemer.spec.js
+++ b/scripts/lib/__tests__/StarterThemer.spec.js
@@ -985,6 +985,8 @@ describe('applyThemeToStarter on a 2D starter', () => {
     const slot = theme.slots['2d.side.player'];
     // 16 pixels tiles, for a starter built on 64 pixels tiles.
     slot.tileSize = 16;
+    slot.width = 32;
+    slot.height = 32;
     const project = makeProject();
     applyThemeToStarter(project, makeThemeSlots(), theme, options);
     /** @type {any} */
@@ -1007,6 +1009,42 @@ describe('applyThemeToStarter on a 2D starter', () => {
     expect(pixelPlayer.preScale).toBe(2);
   });
 
+  it('halves the scale of grid art wider than an instance with a custom size', () => {
+    const theme = makeTheme();
+    /** @type {any} */
+    const slot = theme.slots['2d.side.player'];
+    slot.tileSize = 16;
+    slot.width = 32;
+    slot.height = 48;
+    slot.objectContent.animations.forEach((/** @type {any} */ animation) => {
+      animation.directions[0].sprites[0].customCollisionMask = [
+        [
+          { x: 0, y: 0 },
+          { x: 32, y: 0 },
+          { x: 32, y: 48 },
+          { x: 0, y: 48 },
+        ],
+      ];
+    });
+    const project = makeProject();
+    Object.assign(project.layouts[0].instances[1], {
+      x: 100,
+      y: 200,
+      width: 64,
+      height: 128,
+    });
+    applyThemeToStarter(project, makeThemeSlots(), theme, options);
+    // 128x192 at the scale of the grid: 64x96, standing on the same bottom.
+    // The origin is at (8, 32) in the art, so the art is drawn at (100, 232).
+    expect(project.layouts[0].instances[1]).toMatchObject({
+      customSize: true,
+      x: 116,
+      y: 296,
+      width: 64,
+      height: 96,
+    });
+  });
+
   it('plays an animation with the theme animation the starter asks for', () => {
     const project = makeProject();
     /** @type {any} */