diff --git a/src/main/java/de/neemann/digital/gui/components/table/TableDialog.java b/src/main/java/de/neemann/digital/gui/components/table/TableDialog.java
index fb0ff162d..6264bc615 100644
--- a/src/main/java/de/neemann/digital/gui/components/table/TableDialog.java
+++ b/src/main/java/de/neemann/digital/gui/components/table/TableDialog.java
@@ -291,6 +291,9 @@ public class TableDialog extends JDialog {
 
         setJMenuBar(bar);
 
+        karnaughMenuAction.setEnabled(undoManager.getActual().getVars().size() <= 4);
+        calculateExpressions();
+
         getContentPane().add(new JScrollPane(table));
         getContentPane().add(statusBar, BorderLayout.SOUTH);
         pack();