diff --git a/public/views/grid-setup.mjs b/public/views/grid-setup.mjs
index 9c39817..3eb0078 100644
--- a/public/views/grid-setup.mjs
+++ b/public/views/grid-setup.mjs
@@ -29,7 +29,7 @@ export class Grid_Setup {
 		this.#canvas = canvas_el;
 		this.#ctx = canvas_el.getContext('2d');
 
-		canvas_el.addEventListener('mousedown',  e => this.#on_down(e));
+		canvas_el.addEventListener('mousedown',  e => { e.preventDefault(); this.#on_down(e); });
 		canvas_el.addEventListener('mousemove',  e => this.#on_move(e));
 		canvas_el.addEventListener('mouseup',    e => this.#on_up(e));
 		canvas_el.addEventListener('mouseleave', () => { this.#drag_idx = -1; this.#panning = false; });
@@ -161,14 +161,19 @@ export class Grid_Setup {
 	#on_down(e, is_touch = false) {
 		if (!this.#corners) return;
 		const sp = this.#screen_pos(e);
+		if (!is_touch && e.button === 1) {
+			// Middle button: pan
+			e.preventDefault();
+			this.#panning = true;
+			this.#pan_last = sp;
+			this.#canvas.style.cursor = 'grabbing';
+			return;
+		}
+		if (!is_touch && e.button !== 0) { return; }
 		const hit = this.#find_handle(sp);
 		if (hit !== -1) {
 			this.#drag_idx = hit;
 			this.#drag_prev_img = this.#world_to_img(this.#to_world(sp));
-		} else {
-			this.#panning = true;
-			this.#pan_last = sp;
-			if (!is_touch) { this.#canvas.style.cursor = 'grabbing'; }
 		}
 	}