diff --git a/build.sh b/build.sh
index c3417a1..78f2fb5 100755
--- a/build.sh
+++ b/build.sh
@@ -189,6 +189,11 @@ source "${SCRIPT_DIR}/common"
 # shellcheck source=scripts/dependencies_check
 source "${SCRIPT_DIR}/dependencies_check"
 
+#check username is valid
+if [[ ! "$FIRST_USER_NAME" =~ ^[a-z][-a-z0-9_]*$ ]]; then
+	echo "Invalid FIRST_USER_NAME: $FIRST_USER_NAME"
+	exit 1
+fi
 
 dependencies_check "${BASE_DIR}/depends"