diff --git a/lib/bricolage/context.rb b/lib/bricolage/context.rb
index cbbca30..7c33858 100644
--- a/lib/bricolage/context.rb
+++ b/lib/bricolage/context.rb
@@ -100,12 +100,23 @@ def load_system_options
 
     def global_variables
       Variables.union(
+        environment_variables,
         builtin_variables,
         load_global_variables,
         @opt_global_variables
       )
     end
 
+    def environment_variables
+      Variables.define {|vars|
+        ENV.each do |name, value|
+          if /\A[A-Z][A-Z0-9_]*\z/ =~ name
+            vars[name] = value
+          end
+        end
+      }
+    end
+
     def builtin_variables
       Variables.define {|vars|
         vars['bricolage_env'] = @environment