1 files changed, 5 insertions, 1 deletions
diff --git a/marshal.c b/marshal.c
index dc0194c8dc..abe3375b34 100644
--- a/marshal.c
+++ b/marshal.c
@@ -1373,7 +1373,11 @@ r_leave(VALUE v, struct load_arg *arg)
 static int
 copy_ivar_i(st_data_t key, st_data_t val, st_data_t arg)
 {
-    rb_ivar_set((VALUE)arg, (ID)key, (VALUE)val);
+    VALUE obj = (VALUE)arg, value = (VALUE)val;
+    ID vid = (ID)key;
+
+    if (!rb_ivar_defined(obj, vid))
+	rb_ivar_set(obj, vid, value);
     return ST_CONTINUE;
 }