diff --git a/middleman-core/lib/middleman-core/renderers/sass.rb b/middleman-core/lib/middleman-core/renderers/sass.rb
index 3b2ad68a..80af2d1a 100644
--- a/middleman-core/lib/middleman-core/renderers/sass.rb
+++ b/middleman-core/lib/middleman-core/renderers/sass.rb
@@ -105,7 +105,7 @@ module Middleman
             filename: eval_file,
             line: line,
             syntax: syntax,
-            custom: { middleman_context: ctx.app }
+            custom: (options[:custom] || {}).merge(middleman_context: ctx.app)
           }
 
           if ctx.is_a?(::Middleman::TemplateContext) && file