diff --git a/build_sysext b/build_sysext
index 823313ef3d..3d28e8627f 100755
--- a/build_sysext
+++ b/build_sysext
@@ -184,15 +184,15 @@ mkdir "${BUILD_DIR}/install-root"
 mkdir "${BUILD_DIR}/workdir"
 mount -t overlay overlay -o lowerdir="${BUILD_DIR}/fs-root${pkginfo_lowerdirs}",upperdir="${BUILD_DIR}/install-root",workdir="${BUILD_DIR}/workdir" "${BUILD_DIR}/install-root"
 
-REPO_BUILD_ID="$(source "${REPO_MANIFESTS_DIR}/version.txt"; echo "$FLATCAR_BUILD_ID")"
-REPO_FLATCAR_VERSION="$(source "${REPO_MANIFESTS_DIR}/version.txt"; echo "$FLATCAR_VERSION")"
+REPO_BUILD_ID=$(source "${REPO_MANIFESTS_DIR}/version.txt"; echo "$FLATCAR_BUILD_ID")
+REPO_FLATCAR_VERSION=$(source "${REPO_MANIFESTS_DIR}/version.txt"; echo "$FLATCAR_VERSION")
 VERSION_BOARD=$(source "${BUILD_DIR}/fs-root/usr/lib/os-release" && echo "$VERSION")
 
-if [ -z "$REPO_BUILD_ID" ] ; then
+if [[ -z $REPO_BUILD_ID ]] ; then
     BASE_SQUASHFS_BUILD_ID=$(source "${BUILD_DIR}/fs-root/usr/lib/os-release" && echo -n "$BUILD_ID")
-    info "This is a dev rebuild of an official release tag: No BUILD ID set in '${REPO_MANIFESTS_DIR}/version.txt'.  Will use base squasfs BUILD ID for version check."
+    info "This is a dev rebuild of an official release tag: No BUILD ID set in '${REPO_MANIFESTS_DIR}/version.txt'.  Will use base squashfs BUILD ID for version check."
     info "Repo root FLATCAR_VERSION is '$REPO_FLATCAR_VERSION', squashfs build ID is '$BASE_SQUASHFS_BUILD_ID'"
-    FLATCAR_VERSION="${REPO_FLATCAR_VERSION}+${BASE_SQUASHFS_BUILD_ID}"
+    FLATCAR_VERSION="${REPO_FLATCAR_VERSION}${BASE_SQUASHFS_BUILD_ID:++}${BASE_SQUASHFS_BUILD_ID}"
     info "Setting FLATCAR_VERSION to '$FLATCAR_VERSION'"
 fi