diff --git a/ChangeLog b/ChangeLog
index 8de7bfc7d2..fd0f41cf3f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+Tue Jul  1 03:05:22 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (read_all): truncate the buffer before appending read data,
+	  instead of truncating before reading.
+	  [ruby-core:55951] [Bug #8625]
+
+Tue Jul  1 03:05:22 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (io_setstrbuf, io_read): should not shorten the given buffer until
+	  read succeeds.  [ruby-core:55951] [Bug #8625]
+
 Mon Jun 30 03:15:59 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* vm.c (core_hash_merge_kwd): should return the result hash, which
diff --git a/io.c b/io.c
index 6deb44187f..e5a4d3b40c 100644
--- a/io.c
+++ b/io.c
@@ -2291,9 +2291,6 @@ io_setstrbuf(VALUE *str, long len)
 	long clen = RSTRING_LEN(s);
 	if (clen >= len) {
 	    rb_str_modify(s);
-	    if (clen != len) {
-		rb_str_set_len(s, len);
-	    }
 	    return;
 	}
 	len -= clen;
@@ -2320,23 +2317,27 @@ read_all(rb_io_t *fptr, long siz, VALUE str)
     int cr;
 
     if (NEED_READCONV(fptr)) {
+	int first = !NIL_P(str);
 	SET_BINARY_MODE(fptr);
 	io_setstrbuf(&str,0);
         make_readconv(fptr, 0);
         while (1) {
             VALUE v;
             if (fptr->cbuf.len) {
+		if (first) rb_str_set_len(str, first = 0);
                 io_shift_cbuf(fptr, fptr->cbuf.len, &str);
             }
             v = fill_cbuf(fptr, 0);
             if (v != MORE_CHAR_SUSPENDED && v != MORE_CHAR_FINISHED) {
                 if (fptr->cbuf.len) {
+		    if (first) rb_str_set_len(str, first = 0);
                     io_shift_cbuf(fptr, fptr->cbuf.len, &str);
                 }
                 rb_exc_raise(v);
             }
             if (v == MORE_CHAR_FINISHED) {
                 clear_readconv(fptr);
+		if (first) rb_str_set_len(str, first = 0);
                 return io_enc_str(str, fptr);
             }
         }
@@ -2807,7 +2808,10 @@ io_read(int argc, VALUE *argv, VALUE io)
 
     GetOpenFile(io, fptr);
     rb_io_check_byte_readable(fptr);
-    if (len == 0) return str;
+    if (len == 0) {
+	io_set_read_length(str, 0);
+	return str;
+    }
 
     READ_CHECK(fptr);
 #if defined(RUBY_TEST_CRLF_ENVIRONMENT) || defined(_WIN32)
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index 115a498474..a7c5b2a39a 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -1224,6 +1224,14 @@ class TestIO < Test::Unit::TestCase
       t.value
       assert_equal("", s)
     end
+    with_pipe do |r, w|
+      s = "xxx"
+      t = Thread.new {r.read(2, s)}
+      Thread.pass until t.stop?
+      t.kill
+      t.value
+      assert_equal("xxx", s)
+    end
   end
 
   def test_write_nonblock
diff --git a/test/ruby/test_pipe.rb b/test/ruby/test_pipe.rb
index 34f231ad8c..bcea91bebb 100644
--- a/test/ruby/test_pipe.rb
+++ b/test/ruby/test_pipe.rb
@@ -13,4 +13,17 @@ class TestPipe < Test::Unit::TestCase
       r.close
     end
   end
+  class WithConversion < self
+    def open_file(content)
+      r, w = IO.pipe
+      w << content
+      w.close
+      r.set_encoding("us-ascii:utf-8")
+      begin
+        yield r
+      ensure
+        r.close
+      end
+    end
+  end
 end
diff --git a/version.h b/version.h
index cc54704b1b..535f2e6122 100644
--- a/version.h
+++ b/version.h
@@ -1,6 +1,6 @@
 #define RUBY_VERSION "2.1.2"
 #define RUBY_RELEASE_DATE "2014-07-01"
-#define RUBY_PATCHLEVEL 158
+#define RUBY_PATCHLEVEL 159
 
 #define RUBY_RELEASE_YEAR 2014
 #define RUBY_RELEASE_MONTH 7