Index: trunk/src/org/openstreetmap/josm/data/validation/tests/OpeningHourTest.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/validation/tests/OpeningHourTest.java	(revision 15327)
+++ trunk/src/org/openstreetmap/josm/data/validation/tests/OpeningHourTest.java	(revision 15328)
@@ -21,4 +21,5 @@
 import org.openstreetmap.josm.data.validation.TestError;
 import org.openstreetmap.josm.gui.Notification;
+import org.openstreetmap.josm.gui.util.GuiHelper;
 import org.openstreetmap.josm.io.CachedFile;
 import org.openstreetmap.josm.tools.LanguageInfo;
@@ -250,5 +251,5 @@
         } catch (ScriptException | NoSuchMethodException ex) {
             Logging.error(ex);
-            new Notification(Utils.getRootCause(ex).getMessage()).setIcon(JOptionPane.ERROR_MESSAGE).show();
+            GuiHelper.runInEDT(() -> new Notification(Utils.getRootCause(ex).getMessage()).setIcon(JOptionPane.ERROR_MESSAGE).show());
         }
         return errors;