diff --git a/trio/_version.py b/trio/_version.py
index f6370253c9..0a9521951b 100644
--- a/trio/_version.py
+++ b/trio/_version.py
@@ -1,3 +1,3 @@
 # This file is imported from __init__.py and exec'd from setup.py
 
-__version__ = "0.5.0"
+__version__ = "0.5.0+dev"