diff --git a/src/net/http/httputil/dump.go b/src/net/http/httputil/dump.go
index 81c2795156..c97be066d7 100644
--- a/src/net/http/httputil/dump.go
+++ b/src/net/http/httputil/dump.go
@@ -24,7 +24,7 @@ import (
 // It returns an error if the initial slurp of all bytes fails. It does not attempt
 // to make the returned ReadClosers have identical error-matching behavior.
 func drainBody(b io.ReadCloser) (r1, r2 io.ReadCloser, err error) {
-	if b == http.NoBody {
+	if b == nil || b == http.NoBody {
 		// No copying needed. Preserve the magic sentinel meaning of NoBody.
 		return http.NoBody, http.NoBody, nil
 	}
@@ -60,16 +60,28 @@ func (b neverEnding) Read(p []byte) (n int, err error) {
 	return len(p), nil
 }
 
+// outGoingLength is a copy of the unexported
+// (*http.Request).outgoingLength method.
+func outgoingLength(req *http.Request) int64 {
+	if req.Body == nil || req.Body == http.NoBody {
+		return 0
+	}
+	if req.ContentLength != 0 {
+		return req.ContentLength
+	}
+	return -1
+}
+
 // DumpRequestOut is like DumpRequest but for outgoing client requests. It
 // includes any headers that the standard http.Transport adds, such as
 // User-Agent.
 func DumpRequestOut(req *http.Request, body bool) ([]byte, error) {
 	save := req.Body
 	dummyBody := false
-	if !body || req.Body == nil {
-		req.Body = nil
-		if req.ContentLength != 0 {
-			req.Body = ioutil.NopCloser(io.LimitReader(neverEnding('x'), req.ContentLength))
+	if !body {
+		contentLength := outgoingLength(req)
+		if contentLength != 0 {
+			req.Body = ioutil.NopCloser(io.LimitReader(neverEnding('x'), contentLength))
 			dummyBody = true
 		}
 	} else {
diff --git a/src/net/http/httputil/dump_test.go b/src/net/http/httputil/dump_test.go
index 85731d36f4..ead56bc172 100644
--- a/src/net/http/httputil/dump_test.go
+++ b/src/net/http/httputil/dump_test.go
@@ -17,6 +17,12 @@ import (
 	"testing"
 )
 
+type eofReader struct{}
+
+func (n eofReader) Close() error { return nil }
+
+func (n eofReader) Read([]byte) (int, error) { return 0, io.EOF }
+
 type dumpTest struct {
 	// Either Req or GetReq can be set/nil but not both.
 	Req    *http.Request
@@ -204,6 +210,29 @@ var dumpTests = []dumpTest{
 			"Content-Length: 0\r\n" +
 			"Accept-Encoding: gzip\r\n\r\n",
 	},
+
+	// Issue 34504: a non-nil Body without ContentLength set should be chunked
+	{
+		Req: &http.Request{
+			Method: "PUT",
+			URL: &url.URL{
+				Scheme: "http",
+				Host:   "post.tld",
+				Path:   "/test",
+			},
+			ContentLength: 0,
+			Proto:         "HTTP/1.1",
+			ProtoMajor:    1,
+			ProtoMinor:    1,
+			Body:          &eofReader{},
+		},
+		NoBody: true,
+		WantDumpOut: "PUT /test HTTP/1.1\r\n" +
+			"Host: post.tld\r\n" +
+			"User-Agent: Go-http-client/1.1\r\n" +
+			"Transfer-Encoding: chunked\r\n" +
+			"Accept-Encoding: gzip\r\n\r\n",
+	},
 }
 
 func TestDumpRequest(t *testing.T) {