diff --git a/mitmproxy/io_compat.py b/mitmproxy/io_compat.py
index d299b973a..c12d2098d 100644
--- a/mitmproxy/io_compat.py
+++ b/mitmproxy/io_compat.py
@@ -88,12 +88,12 @@ def convert_019_100(data):
 
 def convert_100_200(data):
     data["version"] = (2, 0, 0)
-    data["client_conn"]["mitmcert"] = None
     return data
 
 
 def convert_200_300(data):
     data["version"] = (3, 0, 0)
+    data["client_conn"]["mitmcert"] = None
     return data