--- a/devtools/server/actors/highlighters/measuring-tool.js
+++ b/devtools/server/actors/highlighters/measuring-tool.js
@@ -514,18 +514,18 @@ MeasuringToolHighlighter.prototype = {
         break;
       case "mousemove":
         ({ scrollX, scrollY, innerWidth, innerHeight } = this.env.window);
         x = event.clientX + scrollX;
         y = event.clientY + scrollY;
 
         let { coords } = this;
 
-        x = Math.min(innerWidth + scrollX - 1, Math.max(0 + scrollX, x));
-        y = Math.min(innerHeight + scrollY, Math.max(1 + scrollY, y));
+        x = Math.min(innerWidth + scrollX, Math.max(scrollX, x));
+        y = Math.min(innerHeight + scrollY, Math.max(scrollY, y));
 
         this.setSize(x - coords.x, y - coords.y);
 
         let type = this._isDragging ? "size" : "position";
 
         this.showLabel(type);
         break;
       case "mouseleave":