diff --git a/intelmq/bots/experts/filter/expert.py b/intelmq/bots/experts/filter/expert.py
index 686744581..c716f19fd 100644
--- a/intelmq/bots/experts/filter/expert.py
+++ b/intelmq/bots/experts/filter/expert.py
@@ -148,10 +148,12 @@ def doFilter(self, event, key, condition):
             return self.equalsFilter(event, key, condition)
 
     def equalsFilter(self, event, key, value):
+        self.logger.debug('Equality check: %r (event value) == %r (filter value).', event.get(key), value)
         return (key in event and
                 event.get(key) == value)
 
     def regexSearchFilter(self, event, key):
+        self.logger.debug('Regex filter: Matching %r against %r.', str(event.get(key)), self.filter_value)
         if key in event:
             return self.regex.search(str(event.get(key)))
         else: