src/pkg/bufio/bufio.go      | 17 +++++++++++------
 src/pkg/bufio/bufio_test.go | 22 ++++++++++++++++++++++

diff --git a/src/pkg/bufio/bufio.go b/src/pkg/bufio/bufio.go
index df3501f2ca1776dfae856aa2bfa8c4e3002aa803..10e12d42be8440d63805984cfe35f408473b2a54 100644
--- a/src/pkg/bufio/bufio.go
+++ b/src/pkg/bufio/bufio.go
@@ -585,23 +585,28 @@ 		}
 	}
 	var m int
 	for {
+		if b.Available() == 0 {
+			if err1 := b.Flush(); err1 != nil {
+				return n, err1
+			}
+		}
 		m, err = r.Read(b.buf[b.n:])
 		if m == 0 {
 			break
 		}
 		b.n += m
 		n += int64(m)
-		if b.Available() == 0 {
-			if err1 := b.Flush(); err1 != nil {
-				return n, err1
-			}
-		}
 		if err != nil {
 			break
 		}
 	}
 	if err == io.EOF {
-		err = nil
+		// If we filled the buffer exactly, flush pre-emptively.
+		if b.Available() == 0 {
+			err = b.Flush()
+		} else {
+			err = nil
+		}
 	}
 	return n, err
 }
diff --git a/src/pkg/bufio/bufio_test.go b/src/pkg/bufio/bufio_test.go
index 79ed0f178e036ccab1ffb7b2fe166a6138267ecc..9fcbfda68dc2c37592bfd921cfd882c4571cd4d1 100644
--- a/src/pkg/bufio/bufio_test.go
+++ b/src/pkg/bufio/bufio_test.go
@@ -847,6 +847,10 @@ 			if n, err := w.ReadFrom(r); err != nil || n != int64(len(input)) {
 				t.Errorf("ws[%d],rs[%d]: w.ReadFrom(r) = %d, %v, want %d, nil", wi, ri, n, err, len(input))
 				continue
 			}
+			if err := w.Flush(); err != nil {
+				t.Errorf("Flush returned %v", err)
+				continue
+			}
 			if got, want := b.String(), string(input); got != want {
 				t.Errorf("ws[%d], rs[%d]:\ngot  %q\nwant %q\n", wi, ri, got, want)
 			}
@@ -1000,6 +1004,24 @@ 		t.Fatalf("3rd Read with buffer = %v; want nil", err)
 	}
 	if r.nread != 2 {
 		t.Errorf("num reads = %d; want 2", r.nread)
+	}
+}
+
+// Test for golang.org/issue/5947
+func TestWriterReadFromWhileFull(t *testing.T) {
+	buf := new(bytes.Buffer)
+	w := NewWriterSize(buf, 10)
+
+	// Fill buffer exactly.
+	n, err := w.Write([]byte("0123456789"))
+	if n != 10 || err != nil {
+		t.Fatalf("Write returned (%v, %v), want (10, nil)", n, err)
+	}
+
+	// Use ReadFrom to read in some data.
+	n2, err := w.ReadFrom(strings.NewReader("abcdef"))
+	if n2 != 6 || err != nil {
+		t.Fatalf("ReadFrom returned (%v, %v), want (6, nil)", n, err)
 	}
 }