diff --git a/test/test_helper.rb b/test/test_helper.rb
index 013b3af2..3309e308 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-GC.auto_compact = true if GC.respond_to?(:auto_compact=)
+GC.auto_compact = true if !defined?(MimeMagic) && GC.respond_to?(:auto_compact=) # https://github.com/mimemagicrb/mimemagic/issues/166
 
 if ENV.key?("CI")
   require "simplecov"