3 files changed, 14 insertions, 1 deletions
diff --git a/ChangeLog b/ChangeLog
index 55a42519b6..a856b4deee 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Jun 11 18:02:09 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (io_getc): should be 7bit if ascii.  fixes #4557
+
 Sat Jun 11 16:52:16 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* numeric.c (rb_enc_uint_chr): fix message format. Bug#4869
diff --git a/io.c b/io.c
index 50892e83e6..3618ac2321 100644
--- a/io.c
+++ b/io.c
@@ -2887,7 +2887,7 @@ io_getc(rb_io_t *fptr, rb_encoding *enc)
 	}
 	else {
 	    io_shift_cbuf(fptr, MBCLEN_CHARFOUND_LEN(r), &str);
-	    cr = ENC_CODERANGE_VALID;
+	    cr = ISASCII(r) ? ENC_CODERANGE_7BIT : ENC_CODERANGE_VALID;
 	}
 	str = io_enc_str(str, fptr);
 	ENC_CODERANGE_SET(str, cr);
diff --git a/test/ruby/test_io_m17n.rb b/test/ruby/test_io_m17n.rb
index 86d45a50ae..091b04a5af 100644
--- a/test/ruby/test_io_m17n.rb
+++ b/test/ruby/test_io_m17n.rb
@@ -2060,5 +2060,14 @@ EOT
            r.close
          end)
   end
+
+  def test_getc_ascii_only
+    bug4557 = '[ruby-core:35630]'
+    c = with_tmpdir {
+      open("a", "wb") {|f| f.puts "a"}
+      open("a", "rt") {|f| f.getc}
+    }
+    assert(c.ascii_only?, "should be ascii_only #{bug4557}")
+  end
 end