diff --git a/cowrie/core/output.py b/cowrie/core/output.py
index cb9bc1e..dbff703 100644
--- a/cowrie/core/output.py
+++ b/cowrie/core/output.py
@@ -137,6 +137,7 @@ class Output(object):
         if 'format' in ev and (not 'message' in ev or ev['message'] == () ):
             try:
                 ev['message'] = ev['format'] % ev
+                del ev['format']
             except:
                 pass