diff --git a/setup.py b/setup.py
index 467a065b1..f212ee20f 100644
--- a/setup.py
+++ b/setup.py
@@ -1,7 +1,11 @@
 import os
 from setuptools import setup
 
-version = os.environ.get("VERSION", "1.0.dev0")
+# Source builds stamp a version ABOVE every date release. Intra-family deps
+# carry `>=` floors, so a low dev stamp (the old "1.0.dev0") makes a local
+# checkout unsatisfiable against its own siblings. Release builds always set
+# VERSION explicitly, so this default is never published.
+version = os.environ.get("VERSION", "9999.0.0.dev0")
 
 setup(
     version=version,