diff --git a/lib/sass/gem_package_importer.rb b/lib/sass/gem_package_importer.rb
index fc27f0fd..11a25149 100644
--- a/lib/sass/gem_package_importer.rb
+++ b/lib/sass/gem_package_importer.rb
@@ -9,8 +9,9 @@ def find_file_url(url, _canonicalize_context)
 
       library, _, path = url[4..].partition(/[?#]/).first.partition('/')
       gem_dir = Gem::Dependency.new(library).to_spec.gem_dir
+      gem_dir = "/#{gem_dir}" unless gem_dir.start_with?('/')
 
-      "file://#{'/' unless gem_dir.start_with?('/')}#{gem_dir.gsub(/[?#]/, { '?' => '%3F', '#' => '%23' })}/#{path}"
+      "file://#{gem_dir.gsub(/[?#%]/, { '?' => '%3F', '#' => '%23', '%' => '%25' })}/#{path}"
     rescue Gem::MissingSpecError
       nil
     end