diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index ad70dfad..e372feee 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -26,11 +26,14 @@ jobs:
         ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
         os: [ ubuntu-latest, macos-latest, windows-latest ]
         include:
-          # jruby is broken with "undefined method 'init_struct'"
+          # jruby is broken with "undefined method 'init_data'"
           # https://github.com/ruby/psych/actions/runs/15434465445/job/43438083198?pr=734
           - { os: windows-latest, ruby: jruby-head }
           - { os: macos-latest, ruby: jruby-head }
           - { os: ubuntu-latest, ruby: jruby-head }
+          # Needs truffleruby-head for rb_struct_initialize() (which truffleruby 25.0 does not have)
+          - { os: ubuntu-latest, ruby: truffleruby-head }
+          - { os: macos-latest, ruby: truffleruby-head }
           - { os: windows-latest, ruby: ucrt }
           - { os: windows-latest, ruby: mingw }
           - { os: windows-latest, ruby: mswin }
diff --git a/Gemfile b/Gemfile
index 6185df02..19673236 100644
--- a/Gemfile
+++ b/Gemfile
@@ -7,4 +7,5 @@ group :development do
   gem 'ruby-maven', :platforms => :jruby
   gem 'test-unit'
   gem 'test-unit-ruby-core', ">= 1.0.7"
+  gem 'power_assert', '~> 2.0' if RUBY_VERSION < '3.0' # https://github.com/ruby/power_assert/pull/61
 end
diff --git a/ext/psych/psych_to_ruby.c b/ext/psych/psych_to_ruby.c
index d473a5f8..0132b2c9 100644
--- a/ext/psych/psych_to_ruby.c
+++ b/ext/psych/psych_to_ruby.c
@@ -10,7 +10,11 @@ static VALUE build_exception(VALUE self, VALUE klass, VALUE mesg)
 {
     VALUE e = rb_obj_alloc(klass);
 
+#ifdef TRUFFLERUBY
+    rb_exc_set_message(e, mesg);
+#else
     rb_iv_set(e, "mesg", mesg);
+#endif
 
     return e;
 }
@@ -24,12 +28,9 @@ static VALUE path2class(VALUE self, VALUE path)
     return rb_path_to_class(path);
 }
 
-static VALUE init_struct(VALUE self, VALUE data, VALUE attrs)
+static VALUE init_data(VALUE self, VALUE data, VALUE values)
 {
-    VALUE args = rb_ary_new2(1);
-    rb_ary_push(args, attrs);
-    rb_struct_initialize(data, args);
-
+    rb_struct_initialize(data, values);
     return data;
 }
 
@@ -42,7 +43,7 @@ void Init_psych_to_ruby(void)
     VALUE visitor   = rb_define_class_under(visitors, "Visitor", rb_cObject);
     cPsychVisitorsToRuby = rb_define_class_under(visitors, "ToRuby", visitor);
 
-    rb_define_private_method(cPsychVisitorsToRuby, "init_struct", init_struct, 2);
+    rb_define_private_method(cPsychVisitorsToRuby, "init_data", init_data, 2);
     rb_define_private_method(cPsychVisitorsToRuby, "build_exception", build_exception, 2);
     rb_define_private_method(class_loader, "path2class", path2class, 1);
 }
diff --git a/lib/psych/visitors/to_ruby.rb b/lib/psych/visitors/to_ruby.rb
index 580a74e9..2814ce1a 100644
--- a/lib/psych/visitors/to_ruby.rb
+++ b/lib/psych/visitors/to_ruby.rb
@@ -219,7 +219,8 @@ def visit_Psych_Nodes_Mapping o
             revive_data_members(members, o)
           end
           data ||= allocate_anon_data(o, members)
-          init_struct(data, **members)
+          values = data.members.map { |m| members[m] }
+          init_data(data, values)
           data.freeze
           data