Index: src/org/openstreetmap/josm/gui/preferences/PreferenceTabbedPane.java
===================================================================
--- src/org/openstreetmap/josm/gui/preferences/PreferenceTabbedPane.java	(revision 17315)
+++ src/org/openstreetmap/josm/gui/preferences/PreferenceTabbedPane.java	(working copy)
@@ -575,6 +575,7 @@
     private int computeMaxTabWidth() {
         FontMetrics fm = getFontMetrics(getFont());
         return settings.stream().filter(x -> x instanceof TabPreferenceSetting)
+                .filter(x -> ((TabPreferenceSetting) x).getTitle() != null)
                 .mapToInt(x -> fm.stringWidth(((TabPreferenceSetting) x).getTitle())).max().orElse(120);
     }