1 files changed, 1 insertions, 0 deletions
diff --git a/string.c b/string.c
index d83913c0ee..41d697bce0 100644
--- a/string.c
+++ b/string.c
@@ -1252,6 +1252,7 @@ rb_str_subpat_set(str, re, nth, val)
     }
     end = RMATCH(match)->END(nth);
     len = end - start;
+    rb_str_modify(str);
     rb_str_update(str, start, len, val);
 }