1 files changed, 3 insertions, 0 deletions
diff --git a/lib/puppet/type/user.rb b/lib/puppet/type/user.rb
index 48e35f2c8..71507d172 100755
--- a/lib/puppet/type/user.rb
+++ b/lib/puppet/type/user.rb
@@ -220,6 +220,9 @@ module Puppet
                 if value =~ /^\d+$/
                     raise ArgumentError, "Group names must be provided, not numbers"
                 end
+                if value.include?(",")
+                    raise ArgumentError, "Group names must be provided as an array, not a comma-separated list"
+                end
             end
         end