diff --git a/pyfpdb/Filters.py b/pyfpdb/Filters.py
index 06935e50..9179caac 100644
--- a/pyfpdb/Filters.py
+++ b/pyfpdb/Filters.py
@@ -158,6 +158,7 @@ class Filters(threading.Thread):
         self.type = None # ring/tour
         self.types = {}  # list of all ring/tour values
 
+        self.num_limit_types = 0
         self.fillLimitsFrame(vbox, self.display)
         limitsFrame.add(vbox)