diff --git a/spec/bundler/support/activate.rb b/spec/bundler/support/activate.rb
index e19a6d0ed1..143b77833d 100644
--- a/spec/bundler/support/activate.rb
+++ b/spec/bundler/support/activate.rb
@@ -5,5 +5,5 @@ Gem.instance_variable_set(:@ruby, ENV["RUBY"]) if ENV["RUBY"]
 
 require_relative "path"
 bundler_gemspec = Spec::Path.loaded_gemspec
-bundler_gemspec.instance_variable_set(:@full_gem_path, Spec::Path.source_root)
+bundler_gemspec.instance_variable_set(:@full_gem_path, Spec::Path.source_root.to_s)
 bundler_gemspec.activate if bundler_gemspec.respond_to?(:activate)