diff --git a/Dockerfile b/Dockerfile
index 30f54a4d0..8c351ad7f 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -27,8 +27,8 @@ ARG PATCH_LIST
 ARG INSTALL_TYPE=source
 
 # build arguments for source build customization
-ARG UPPER_CONSTRAINTS_FILE
 ARG IRONIC_SOURCE=bugfix/25.0
+ARG UPPER_CONSTRAINTS_FILE=upper-constraints.txt
 ARG IRONIC_LIB_SOURCE
 ARG SUSHY_SOURCE
 
diff --git a/prepare-image.sh b/prepare-image.sh
index 62942ceac..7ac510e53 100755
--- a/prepare-image.sh
+++ b/prepare-image.sh
@@ -47,7 +47,7 @@ if [[ "$INSTALL_TYPE" == "source" ]]; then
 
     # NOTE(elfosardo): if the content of the upper-constraints file is empty,
     # we give as assumed that we're on the master branch
-    if [[ ! -f "${UPPER_CONSTRAINTS_PATH}" ]]; then
+    if [[ ! -s "${UPPER_CONSTRAINTS_PATH}" ]]; then
         UPPER_CONSTRAINTS_PATH="/tmp/upper-constraints.txt"
         curl -L https://releases.openstack.org/constraints/upper/master -o "${UPPER_CONSTRAINTS_PATH}"
     fi