diff --git a/mitmproxy/version.py b/mitmproxy/version.py
index f02be7299..e4842b025 100644
--- a/mitmproxy/version.py
+++ b/mitmproxy/version.py
@@ -2,7 +2,7 @@ import os
 import subprocess
 import sys
 
-VERSION = "12.1.1"
+VERSION = "13.0.0.dev"
 MITMPROXY = "mitmproxy " + VERSION
 
 # Serialization format version. This is displayed nowhere, it just needs to be incremented by one