diff --git a/templates/nodepool-builder.ssl.vhost.erb b/templates/nodepool-builder.ssl.vhost.erb
index ddfb090..c4e9e4f 100644
--- a/templates/nodepool-builder.ssl.vhost.erb
+++ b/templates/nodepool-builder.ssl.vhost.erb
@@ -16,10 +16,13 @@
 
   SSLEngine on
 
-  SSLCertificateFile      <%= scope.lookupvar("nodepool::builder::ssl_cert_file") %>
-  SSLCertificateKeyFile   <%= scope.lookupvar("nodepool::builder::ssl_key_file") %>
-  <% if scope.lookupvar("nodepool::builder::ssl_chain_file") != "" %>
-    SSLCertificateChainFile <%= scope.lookupvar("nodepool::builder::ssl_chain_file") %>
+  SSLCertificateFile      <%= @ssl_cert_file %>
+  SSLCertificateKeyFile   <%= @ssl_key_file %>
+  <%# The original default was '' -%>
+  <%# scope.lookupvar returns nil for an undefined variable in puppet 4 -%>
+  <%# scope.lookupvar returns :undef for an undefined variable in puppet 3 -%>
+  <% unless ['', nil, :undef].include?@ssl_chain_file %>
+    SSLCertificateChainFile <%= @ssl_chain_file %>
   <% end %>
 
   DocumentRoot <%= scope.lookupvar("nodepool::builder::build_log_document_root") %>