diff --git a/ext/smarter_json/smarter_json.c b/ext/smarter_json/smarter_json.c
index 5852635..7bf91ed 100644
--- a/ext/smarter_json/smarter_json.c
+++ b/ext/smarter_json/smarter_json.c
@@ -1629,9 +1629,16 @@ static VALUE fj_parse_c(VALUE self, VALUE input, VALUE opts) {
 
 void Init_smarter_json(void) {
   mSmarterJSON = rb_define_module("SmarterJSON");
+
+  rb_global_variable(&cParseError);
   cParseError = rb_const_get(mSmarterJSON, rb_intern("ParseError"));
+
+  rb_global_variable(&cEncodingError);
   cEncodingError = rb_const_get(mSmarterJSON, rb_intern("EncodingError"));
+
+  rb_global_variable(&cWarning);
   cWarning = rb_const_get(mSmarterJSON, rb_intern("Warning"));
+
   fj_bigdecimal_id = rb_intern("BigDecimal");
   fj_to_sym_id = rb_intern("to_sym");
   fj_key_p_id = rb_intern("key?");
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 6dcdb87..39c1508 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -7,6 +7,16 @@
 
 require "smarter_json"
 
+if GC.respond_to?(:verify_compaction_references)
+  # This method was added in Ruby 3.0.0. Calling it this way asks the GC to
+  # move objects around, helping to find object movement bugs.
+  begin
+    GC.verify_compaction_references(expand_heap: true, toward: :empty)
+  rescue NotImplementedError, ArgumentError
+    # Some platforms don't support compaction
+  end
+end
+
 RSpec.configure do |config|
   # Enable flags like --only-failures and --next-failure
   config.example_status_persistence_file_path = ".rspec_status"