Index: src/main/java/common/javax/swing/plaf/basic/BasicTabbedPaneUI.java =================================================================== --- src/main/java/common/javax/swing/plaf/basic/BasicTabbedPaneUI.java (revision 494382) +++ src/main/java/common/javax/swing/plaf/basic/BasicTabbedPaneUI.java (working copy) @@ -895,6 +895,10 @@ } protected JButton createScrollButton(final int direction) { + if (direction != NORTH && direction != SOUTH && direction != EAST && direction != WEST) { + throw new IllegalArgumentException(); + } + return new ScrollButton(direction); }