1 files changed, 10 insertions, 0 deletions
diff --git a/transcode.c b/transcode.c
index 4c3a273e7a..045ce2e118 100644
--- a/transcode.c
+++ b/transcode.c
@@ -2805,6 +2805,10 @@ str_encode_bang(int argc, VALUE *argv, VALUE str)
     encidx = str_transcode(argc, argv, &newstr);
 
     if (encidx < 0) return str;
+    if (newstr == str) {
+	rb_enc_associate_index(str, encidx);
+	return str;
+    }
     rb_str_shared_replace(str, newstr);
     return str_encode_associate(str, encidx);
 }
@@ -2831,6 +2835,10 @@ static VALUE encoded_dup(VALUE newstr, VALUE str, int encidx);
  *  in the source encoding. The last form by default does not raise
  *  exceptions but uses replacement strings.
  *
+ *  Please note that conversion from an encoding +enc+ to the
+ *  same encoding +enc+ is a no-op, i.e. the receiver is returned without
+ *  any changes, and no exceptions are raised, even if there are invalid bytes.
+ *
  *  The +options+ Hash gives details for conversion and can have the following
  *  keys:
  *
@@ -2891,6 +2899,8 @@ encoded_dup(VALUE newstr, VALUE str, int encidx)
     if (encidx < 0) return rb_str_dup(str);
     if (newstr == str) {
 	newstr = rb_str_dup(str);
+	rb_enc_associate_index(newstr, encidx);
+	return newstr;
     }
     else {
 	RBASIC(newstr)->klass = rb_obj_class(str);