diff --git a/Library/Homebrew/resource_auditor.rb b/Library/Homebrew/resource_auditor.rb
index 86a13bea59..4ef3afb951 100644
--- a/Library/Homebrew/resource_auditor.rb
+++ b/Library/Homebrew/resource_auditor.rb
@@ -117,9 +117,11 @@ module Homebrew
         pypi_package_name, = File.basename(path).split("-", 2)
       else
         url =~ %r{/(?<package_name>[^/]+)-}
-        pypi_package_name = Regexp.last_match(:package_name).to_s.gsub(/[_.]/, "-")
+        pypi_package_name = Regexp.last_match(:package_name).to_s
       end
 
+      pypi_package_name.gsub!(/[_.]/, "-")
+
       return if name.casecmp(pypi_package_name).zero?
 
       problem "resource name should be `#{pypi_package_name}` to match the PyPI package name"