1 files changed, 1 insertions, 0 deletions
diff --git a/hash.c b/hash.c
index cc58f608cc..513eeb4347 100644
--- a/hash.c
+++ b/hash.c
@@ -333,6 +333,7 @@ static VALUE
 rb_hash_set_default(hash, ifnone)
     VALUE hash, ifnone;
 {
+    rb_hash_modify(hash);
     RHASH(hash)->ifnone = ifnone;
     return hash;
 }