diff --git a/lib/iris/__init__.py b/lib/iris/__init__.py
index e31c7b58d7..ff4e7b7a28 100644
--- a/lib/iris/__init__.py
+++ b/lib/iris/__init__.py
@@ -106,7 +106,7 @@ def callback(cube, field, filename):
 
 
 # Iris revision.
-__version__ = "3.1.dev0"
+__version__ = "3.1a0"
 
 # Restrict the names imported when using "from iris import *"
 __all__ = [