diff --git a/mrbgems/mruby-os-memsize/src/memsize.c b/mrbgems/mruby-os-memsize/src/memsize.c
index 9206a8ac5..c35a38006 100644
--- a/mrbgems/mruby-os-memsize/src/memsize.c
+++ b/mrbgems/mruby-os-memsize/src/memsize.c
@@ -148,6 +148,7 @@ os_memsize_of_object(mrb_state* mrb, mrb_value obj)
     case MRB_TT_BIGINT:
 #if defined(MRB_USE_BIGINT)
       size += mrb_bint_memsize(obj);
+      /* fall through */
 #endif
     case MRB_TT_DATA:
     case MRB_TT_ISTRUCT: