diff --git a/src/gui/bubble-bar.vala b/src/gui/bubble-bar.vala
index 026c456..dfb795e 100644
--- a/src/gui/bubble-bar.vala
+++ b/src/gui/bubble-bar.vala
@@ -29,7 +29,7 @@ class TheCatTools.GUI.BoubleBar : Gtk.DrawingArea, Gtk.Orientable {
         if (res > 90)
             res = 180 - res;
         if (res < -90)
-            res = -180 + res;
+            res = -180 - res;
         return res.clamp (adjustment.lower, adjustment.upper);
     }