diff --git a/lib/middleman-autoprefixer/extension.rb b/lib/middleman-autoprefixer/extension.rb
index 79c6025..b980e0b 100644
--- a/lib/middleman-autoprefixer/extension.rb
+++ b/lib/middleman-autoprefixer/extension.rb
@@ -65,7 +65,7 @@ def process(response, path)
 
         def prefix(content)
           config = {}
-          config[:browsers] = Array(@browsers)
+          config[:browsers] = Array(@browsers) unless @browsers.nil?
           config[:cascade]  = @cascade unless @cascade.nil?
 
           ::AutoprefixerRails.process(content, config).css