diff --git a/include/mruby/internal.h b/include/mruby/internal.h
index a180f6f77..9f8453eaa 100644
--- a/include/mruby/internal.h
+++ b/include/mruby/internal.h
@@ -144,7 +144,7 @@ mrb_bool mrb_proc_eql(mrb_state *mrb, mrb_value self, mrb_value other);
 /* range */
 #ifdef MRUBY_RANGE_H
 mrb_value mrb_get_values_at(mrb_state *mrb, mrb_value obj, mrb_int olen, mrb_int argc, const mrb_value *argv, mrb_value (*func)(mrb_state*, mrb_value, mrb_int));
-void mrb_gc_mark_range(mrb_state *mrb, struct RRange *r);
+size_t mrb_gc_mark_range(mrb_state *mrb, struct RRange *r);
 #endif
 
 /* string */
diff --git a/src/gc.c b/src/gc.c
index 848c95f55..fe2ab5e4b 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -687,8 +687,7 @@ gc_mark_children(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
     break;
 
   case MRB_TT_RANGE:
-    mrb_gc_mark_range(mrb, (struct RRange*)obj);
-    children+=2;
+    children += mrb_gc_mark_range(mrb, (struct RRange*)obj);
     break;
 
   case MRB_TT_BREAK:
@@ -705,8 +704,10 @@ gc_mark_children(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
       mrb_gc_mark(mrb, (struct RBasic*)((struct RException*)obj)->mesg);
       children++;
     }
-    mrb_gc_mark(mrb, (struct RBasic*)((struct RException*)obj)->backtrace);
-    children++;
+    if (((struct RException*)obj)->backtrace) {
+      mrb_gc_mark(mrb, (struct RBasic*)((struct RException*)obj)->backtrace);
+      children++;
+    }
     break;
 
   case MRB_TT_BACKTRACE:
diff --git a/src/range.c b/src/range.c
index 367e4c996..cf04ceb31 100644
--- a/src/range.c
+++ b/src/range.c
@@ -437,13 +437,13 @@ mrb_get_values_at(mrb_state *mrb, mrb_value obj, mrb_int olen, mrb_int argc, con
   return result;
 }
 
-void
+size_t
 mrb_gc_mark_range(mrb_state *mrb, struct RRange *r)
 {
-  if (RANGE_INITIALIZED_P(r)) {
-    mrb_gc_mark_value(mrb, RANGE_BEG(r));
-    mrb_gc_mark_value(mrb, RANGE_END(r));
-  }
+  if (!RANGE_INITIALIZED_P(r)) return 0;
+  mrb_gc_mark_value(mrb, RANGE_BEG(r));
+  mrb_gc_mark_value(mrb, RANGE_END(r));
+  return 2;
 }
 
 MRB_API struct RRange*