1 files changed, 1 insertions, 0 deletions
diff --git a/io.c b/io.c
index 17f8d5799a..7f23656049 100644
--- a/io.c
+++ b/io.c
@@ -13098,6 +13098,7 @@ copy_stream_fallback_body(VALUE arg)
     while (1) {
         long numwrote;
         long l;
+        rb_str_make_independent(buf);
         if (stp->copy_length < (rb_off_t)0) {
             l = buflen;
         }