[ruby/stringio] No compatibility check in US-ASCII case

https://github.com/ruby/stringio/commit/59df1c8293

1 files changed, 3 insertions, 2 deletions

diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index 9ab8537ac1..d55af518c7 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -1429,14 +1429,15 @@ strio_write(VALUE self, VALUE str)
     long len, olen;
     rb_encoding *enc, *enc2;
     rb_encoding *const ascii8bit = rb_ascii8bit_encoding();
+    rb_encoding *usascii = 0;
 
     if (!RB_TYPE_P(str, T_STRING))
 	str = rb_obj_as_string(str);
     enc = get_enc(ptr);
     enc2 = rb_enc_get(str);
-    if (enc != enc2 && enc != ascii8bit) {
+    if (enc != enc2 && enc != ascii8bit && enc != (usascii = rb_usascii_encoding())) {
 	VALUE converted = rb_str_conv_enc(str, enc2, enc);
-	if (converted == str && enc2 != ascii8bit) { /* conversion failed */
+	if (converted == str && enc2 != ascii8bit && enc2 != usascii) { /* conversion failed */
 	    rb_enc_check(rb_enc_from_encoding(enc), str);
 	}
 	str = converted;