diff --git a/Library/Homebrew/cli/parser.rb b/Library/Homebrew/cli/parser.rb
index a9537aec1b..d1b0d4ba43 100644
--- a/Library/Homebrew/cli/parser.rb
+++ b/Library/Homebrew/cli/parser.rb
@@ -95,6 +95,7 @@ module Homebrew
       end
 
       def comma_array(name, description: nil)
+        name = name.chomp "="
         description = option_to_description(name) if description.nil?
         process_option(name, description)
         @parser.on(name, OptionParser::REQUIRED_ARGUMENT, Array, *wrap_option_desc(description)) do |list|
diff --git a/Library/Homebrew/dev-cmd/bump-formula-pr.rb b/Library/Homebrew/dev-cmd/bump-formula-pr.rb
index efc7963bbe..510cdc3348 100644
--- a/Library/Homebrew/dev-cmd/bump-formula-pr.rb
+++ b/Library/Homebrew/dev-cmd/bump-formula-pr.rb
@@ -40,7 +40,7 @@ module Homebrew
              description: "Print the pull request URL instead of opening in a browser."
       switch "--no-fork",
              description: "Don't try to fork the repository."
-      comma_array "--mirror=",
+      comma_array "--mirror",
                   description: "Use the specified <URL> as a mirror URL. If <URL> is a comma-separated list "\
                                "of URLs, multiple mirrors will be added."
       flag   "--version=",