diff --git a/bits_helpers/build.py b/bits_helpers/build.py
index 484dad93..cac118dc 100644
--- a/bits_helpers/build.py
+++ b/bits_helpers/build.py
@@ -1105,7 +1105,7 @@ def performPreferCheckWithTempDir(pkg, cmd):
       develPrefix = possibleDevelPrefix
 
     if possibleDevelPrefix:
-      spec["build_family"] = "{}-{}".format(possibleDevelPrefix, args.defaults)
+      spec["build_family"] = "{}-{}".format(possibleDevelPrefix, "_".join(args.defaults))
     else:
       spec["build_family"] = "_".join(args.defaults)
     if spec["package"] == mainPackage: