diff --git a/manifests/init.pp b/manifests/init.pp
index 15ef6de689bd0585d253ed6ebb6335774e5bbaba..7da090307edfa883d72c96023c68b97b13e9c245 100644
--- a/manifests/init.pp
+++ b/manifests/init.pp
@@ -5,7 +5,7 @@
 # @example
 #   include easybuild
 class easybuild (
-  $arch = $easybuild::params::arch,
+  String $arch = $easybuild::params::arch,
 ) {
 
   file { '/etc/easybuild.d':