diff --git a/generate-cookiecutter-products.groovy b/generate-cookiecutter-products.groovy
index ea513b7..29f03fe 100644
--- a/generate-cookiecutter-products.groovy
+++ b/generate-cookiecutter-products.groovy
@@ -347,7 +347,7 @@
                 }
 
                 for (i in common.entries(smc)) {
-                    sh "sed -i 's,export ${i[0]}=.*,export ${i[0]}=\"${i[1]}\",' user_data"
+                    sh "sed -i 's,export ${i[0]}=.*,export ${i[0]}=\${${i[0]}:-\"${i[1]}\"},' user_data"
                 }
 
                 // calculate netmask