src/pkg/http/serve_test.go |  7 +++++++
 src/pkg/http/server.go     | 15 +++++++++++----

diff --git a/src/pkg/http/serve_test.go b/src/pkg/http/serve_test.go
index 1054d4797ca9d66865cdc62a7aceb76c040013c1..dc4594a7908aec8aa6585d675c44c85bdbc87ae2 100644
--- a/src/pkg/http/serve_test.go
+++ b/src/pkg/http/serve_test.go
@@ -12,6 +12,7 @@ 	"bytes"
 	"fmt"
 	. "http"
 	"http/httptest"
+	"io"
 	"io/ioutil"
 	"log"
 	"os"
@@ -494,6 +495,12 @@ 	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
 		_, err := w.Write([]byte("Ignored body"))
 		if err != ErrBodyNotAllowed {
 			t.Errorf("on Write, expected ErrBodyNotAllowed, got %v", err)
+		}
+
+		// Also exercise the ReaderFrom path
+		_, err = io.Copy(w, strings.NewReader("Ignored body"))
+		if err != ErrBodyNotAllowed {
+			t.Errorf("on Copy, expected ErrBodyNotAllowed, got %v", err)
 		}
 	}))
 	defer ts.Close()
diff --git a/src/pkg/http/server.go b/src/pkg/http/server.go
index 4063fad224cf07b513d4e59c2f5a138fd7d410d7..d4638f127c7238fffb455bc64b081237352cbf31 100644
--- a/src/pkg/http/server.go
+++ b/src/pkg/http/server.go
@@ -129,7 +129,7 @@ 	// Flush before checking r.chunking, as Flush will call
 	// WriteHeader if it hasn't been called yet, and WriteHeader
 	// is what sets r.chunking.
 	r.Flush()
-	if !r.chunking {
+	if !r.chunking && r.bodyAllowed() {
 		if rf, ok := r.conn.rwc.(io.ReaderFrom); ok {
 			n, err = rf.ReadFrom(src)
 			r.written += n
@@ -335,6 +335,15 @@ 	w.header.Write(w.conn.buf)
 	io.WriteString(w.conn.buf, "\r\n")
 }
 
+// bodyAllowed returns true if a Write is allowed for this response type.
+// It's illegal to call this before the header has been flushed.
+func (w *response) bodyAllowed() bool {
+	if !w.wroteHeader {
+		panic("")
+	}
+	return w.status != StatusNotModified && w.req.Method != "HEAD"
+}
+
 func (w *response) Write(data []byte) (n int, err os.Error) {
 	if w.conn.hijacked {
 		log.Print("http: response.Write on hijacked connection")
@@ -346,9 +355,7 @@ 	}
 	if len(data) == 0 {
 		return 0, nil
 	}
-
-	if w.status == StatusNotModified || w.req.Method == "HEAD" {
-		// Must not have body.
+	if !w.bodyAllowed() {
 		return 0, ErrBodyNotAllowed
 	}