Index: trunk/src/org/openstreetmap/josm/data/validation/tests/MapCSSTagChecker.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/validation/tests/MapCSSTagChecker.java	(revision 12409)
+++ trunk/src/org/openstreetmap/josm/data/validation/tests/MapCSSTagChecker.java	(revision 12410)
@@ -760,5 +760,5 @@
                     Main.fileWatcher.registerValidatorRule(source);
                 }
-            } catch (IOException | IllegalStateException ex) {
+            } catch (IOException | IllegalStateException | IllegalArgumentException ex) {
                 Main.warn(tr("Failed to add {0} to tag checker", i));
                 Main.warn(ex, false);
Index: trunk/src/org/openstreetmap/josm/gui/mappaint/MapPaintStyles.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/mappaint/MapPaintStyles.java	(revision 12409)
+++ trunk/src/org/openstreetmap/josm/gui/mappaint/MapPaintStyles.java	(revision 12410)
@@ -307,5 +307,5 @@
             try {
                 Main.fileWatcher.registerStyleSource(source);
-            } catch (IOException | IllegalStateException e) {
+            } catch (IOException | IllegalStateException | IllegalArgumentException e) {
                 Main.error(e);
             }