1 files changed, 20 insertions, 0 deletions
diff --git a/src/gc.c b/src/gc.c
index e8523af79..c75a0f9aa 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -833,6 +833,26 @@ root_scan_phase(mrb_state *mrb, mrb_gc *gc)
   }
   /* mark class hierarchy */
   mrb_gc_mark(mrb, (struct RBasic*)mrb->object_class);
+
+  /* mark built-in classes */
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->class_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->module_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->proc_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->string_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->array_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->hash_class);
+
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->float_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->fixnum_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->true_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->false_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->nil_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->symbol_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->kernel_module);
+
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->eException_class);
+  mrb_gc_mark(mrb, (struct RBasic*)mrb->eStandardError_class);
+
   /* mark top_self */
   mrb_gc_mark(mrb, (struct RBasic*)mrb->top_self);
   /* mark exception */