diff --git a/hack/dockerfile/install/rootlesskit.installer b/hack/dockerfile/install/rootlesskit.installer
index 02028f62ec..4b3011115f 100755
--- a/hack/dockerfile/install/rootlesskit.installer
+++ b/hack/dockerfile/install/rootlesskit.installer
@@ -1,7 +1,7 @@
 #!/bin/sh
 
 # When updating, also update go.mod and Dockerfile accordingly.
-: "$ROOTLESSKIT_VERSION:=v3.0.2}"
+: "${ROOTLESSKIT_VERSION:=v3.0.2}"
 
 install_rootlesskit() {
 	case "$1" in