diff --git a/middleman-core/features/gzip.feature b/middleman-core/features/gzip.feature
index 93955a49..18669476 100644
--- a/middleman-core/features/gzip.feature
+++ b/middleman-core/features/gzip.feature
@@ -1,4 +1,3 @@
-@nowindows
 Feature: GZIP assets during build
 
   Scenario: Built assets should be gzipped
@@ -10,8 +9,7 @@ Feature: GZIP assets during build
       | build/javascripts/test.js.gz |
       | build/stylesheets/test.css |
       | build/stylesheets/test.css.gz |
-    When I run `file build/javascripts/test.js.gz`
-    Then the output should contain "gzip"
+    And build/javascripts/test.js.gz should be binary
 
   Scenario: Preview server doesn't change
     Given the Server is running at "gzip-app"
diff --git a/middleman-core/lib/middleman-core/step_definitions/builder_steps.rb b/middleman-core/lib/middleman-core/step_definitions/builder_steps.rb
index eda6467b..ce942284 100644
--- a/middleman-core/lib/middleman-core/step_definitions/builder_steps.rb
+++ b/middleman-core/lib/middleman-core/step_definitions/builder_steps.rb
@@ -71,3 +71,7 @@ end
 Then /^the file "([^"]*)" should contain '([^']*)'$/ do |file, partial_content|
   check_file_content(file, partial_content, true)
 end
+
+And /(.*) should be binary/ do |file|
+  expect(File.binread(File.join(current_dir, file), 2)).to eq(['1F8B'].pack('H*'))
+end