diff --git a/string.c b/string.c
index d7ef9cc9bc..26d03d1835 100644
--- a/string.c
+++ b/string.c
@@ -8459,7 +8459,7 @@ rb_str_each_grapheme_cluster_size(VALUE str, VALUE args, VALUE eobj)
     rb_encoding *enc = rb_enc_from_index(ENCODING_GET(str));
     const char *ptr, *end;
 
-    if (!rb_enc_unicode_p(enc) || single_byte_optimizable(str)) {
+    if (!rb_enc_unicode_p(enc)) {
 	return rb_str_length(str);
     }
 
@@ -8487,7 +8487,7 @@ rb_str_enumerate_grapheme_clusters(VALUE str, VALUE ary)
     rb_encoding *enc = rb_enc_from_index(ENCODING_GET(str));
     const char *ptr, *end;
 
-    if (!rb_enc_unicode_p(enc) || single_byte_optimizable(str)) {
+    if (!rb_enc_unicode_p(enc)) {
 	return rb_str_enumerate_chars(str, ary);
     }
 
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index 1a6d87f11f..014eb5ec15 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -973,6 +973,7 @@ CODE
 
   def test_each_grapheme_cluster
     [
+      "\u{0D 0A}",
       "\u{20 200d}",
       "\u{600 600}",
       "\u{600 20}",