diff --git a/contrib/nightly/create_tarball.sh b/contrib/nightly/create_tarball.sh
index f70da15024..3b595b4c0b 100644
--- a/contrib/nightly/create_tarball.sh
+++ b/contrib/nightly/create_tarball.sh
@@ -34,7 +34,7 @@ gitbranch=$5
 
 # Set this to any value for additional output; typically only when
 # debugging
-debug=1
+: ${debug:=}
 
 # do you want a success mail?
 want_success_mail=1