diff --git a/lib/puppet/type/node_group.rb b/lib/puppet/type/node_group.rb
index 8e5176c..00fb697 100644
--- a/lib/puppet/type/node_group.rb
+++ b/lib/puppet/type/node_group.rb
@@ -123,7 +123,7 @@ def insync?(is)
     desc 'Environment for this group'
     defaultto :production
     validate do |value|
-      raise('Invalid environment name') unless value =~ (%r{\A[a-zA-Z0-9_]+\Z}) || (value == 'agent-specified')
+      raise("Invalid environment name: #{value}") unless value =~ (%r{\A[a-zA-Z0-9_]+\Z}) || (value == 'agent-specified')
     end
   end
   newproperty(:classes) do
diff --git a/spec/unit/puppet/type/node_group_spec.rb b/spec/unit/puppet/type/node_group_spec.rb
index 831961e..d35233a 100644
--- a/spec/unit/puppet/type/node_group_spec.rb
+++ b/spec/unit/puppet/type/node_group_spec.rb
@@ -80,7 +80,7 @@
         name: 'stubname',
         environment: 'not-a-valid-name',
       )
-    }.to raise_error(%r{Invalid environment name})
+    }.to raise_error(%r{Invalid environment name: not-a-valid-name})
   end
 
   it 'allows name with symbols, numbers, and whitespace' do