diff --git a/js/ui/boxpointer.js b/js/ui/boxpointer.js
index 1c459a6ba..b1dfa13e6 100644
--- a/js/ui/boxpointer.js
+++ b/js/ui/boxpointer.js
@@ -438,13 +438,13 @@ var BoxPointer = GObject.registerClass({
                 () => (this._sourceActor = null), this);
         }
 
-        this._arrowAlignment = alignment;
+        this._arrowAlignment = Math.clamp(alignment, 0.0, 1.0);
 
         this.queue_relayout();
     }
 
     setSourceAlignment(alignment) {
-        this._sourceAlignment = alignment;
+        this._sourceAlignment = Math.clamp(alignment, 0.0, 1.0);
 
         if (!this._sourceActor)
             return;