diff --git a/Library/Homebrew/rubocops/lines_cop.rb b/Library/Homebrew/rubocops/lines_cop.rb
index 6c79e1fca1..2b146b79ed 100644
--- a/Library/Homebrew/rubocops/lines_cop.rb
+++ b/Library/Homebrew/rubocops/lines_cop.rb
@@ -281,12 +281,12 @@ module RuboCop
             problem "Use if #{correct} instead of unless #{m.source}"
           end
 
-          # find_instance_method_call(body_node, :build, :with?) do |m|
-          #   next unless unless_modifier?(m.parent)
-          #   correct = m.source.gsub("?", "out?").gsub("unless", "if")
-          #   problem "Use #{correct} instead of unless #{m.source}"
-          # end
-          #
+          find_instance_method_call(body_node, :build, :with?) do |m|
+            next unless unless_modifier?(m.parent)
+            correct = m.source.gsub("?", "out?")
+            problem "Use if #{correct} instead of unless #{m.source}"
+          end
+
           # find_instance_method_call(body_node, :build, :with?) do |m|
           #   next unless negation?(m)
           #   problem "Don't negate 'build.with?': use 'build.without?'"
diff --git a/Library/Homebrew/test/rubocops/lines_cop_spec.rb b/Library/Homebrew/test/rubocops/lines_cop_spec.rb
index 352dc82196..dda1b96e61 100644
--- a/Library/Homebrew/test/rubocops/lines_cop_spec.rb
+++ b/Library/Homebrew/test/rubocops/lines_cop_spec.rb
@@ -643,6 +643,30 @@ describe RuboCop::Cop::FormulaAudit::Miscellaneous do
         expect_offense(expected, actual)
       end
     end
+
+    it "with unless build.with?" do
+      source = <<-EOS.undent
+        class Foo < Formula
+          desc "foo"
+          url 'http://example.com/foo-1.0.tgz'
+          def post_install
+            return unless build.with? "bar"
+          end
+        end
+      EOS
+
+      expected_offenses = [{  message: 'Use if build.without? "bar" instead of unless build.with? "bar"',
+                              severity: :convention,
+                              line: 5,
+                              column: 18,
+                              source: source }]
+
+      inspect_source(cop, source)
+
+      expected_offenses.zip(cop.offenses).each do |expected, actual|
+        expect_offense(expected, actual)
+      end
+    end
   end
   def expect_offense(expected, actual)
     expect(actual.message).to eq(expected[:message])