1 files changed, 9 insertions, 2 deletions

diff --git a/string.c b/string.c
index 9006abdfac..9053835ee2 100644
--- a/string.c
+++ b/string.c
@@ -487,8 +487,15 @@ rb_enc_str_coderange(VALUE str)
     int cr = ENC_CODERANGE(str);
 
     if (cr == ENC_CODERANGE_UNKNOWN) {
-	rb_encoding *enc = STR_ENC_GET(str);
-        cr = coderange_scan(RSTRING_PTR(str), RSTRING_LEN(str), enc);
+	int encidx = ENCODING_GET(str);
+	rb_encoding *enc = rb_enc_from_index(encidx);
+	if (rb_enc_mbminlen(enc) > 1 && rb_enc_dummy_p(enc)) {
+	    cr = ENC_CODERANGE_BROKEN;
+	}
+	else {
+	    cr = coderange_scan(RSTRING_PTR(str), RSTRING_LEN(str),
+				get_actual_encoding(encidx, str));
+	}
         ENC_CODERANGE_SET(str, cr);
     }
     return cr;