diff --git a/ui/jquery.ui.position.js b/ui/jquery.ui.position.js
index d45b24bb16..21c3cef1b1 100644
--- a/ui/jquery.ui.position.js
+++ b/ui/jquery.ui.position.js
@@ -436,7 +436,7 @@ $.ui.position = {
 				}
 			}
 			else if ( overBottom > 0 ) {
-				newOverTop = position.top -  data.collisionPosition.marginTop + myOffset + atOffset + offset - offsetTop;
+				newOverTop = position.top - data.collisionPosition.marginTop + myOffset + atOffset + offset - offsetTop;
 				if ( ( position.top + myOffset + atOffset + offset) > overBottom && ( newOverTop > 0 || abs( newOverTop ) < overBottom ) ) {
 					position.top += myOffset + atOffset + offset;
 				}