diff --git a/Library/Homebrew/Gemfile b/Library/Homebrew/Gemfile
index 1c00b85ab8..a434b3a5c9 100644
--- a/Library/Homebrew/Gemfile
+++ b/Library/Homebrew/Gemfile
@@ -2,11 +2,13 @@
 
 source "https://rubygems.org"
 
+# disallowed gems (should not be used)
+# * nokogiri - use rexml instead for XML parsing
+
 # installed gems (should all be require: false)
 gem "bootsnap", require: false
 gem "byebug", require: false
 gem "minitest", require: false
-gem "nokogiri", require: false
 gem "parallel_tests", require: false
 gem "ronn", require: false
 gem "rspec", require: false
diff --git a/Library/Homebrew/Gemfile.lock b/Library/Homebrew/Gemfile.lock
index a712aef3ec..2a220d3c41 100644
--- a/Library/Homebrew/Gemfile.lock
+++ b/Library/Homebrew/Gemfile.lock
@@ -187,7 +187,6 @@ DEPENDENCIES
   did_you_mean
   mechanize
   minitest
-  nokogiri
   parallel_tests
   patchelf
   plist