diff --git a/src/net/http/request.go b/src/net/http/request.go
index 8467decc18..67976da103 100644
--- a/src/net/http/request.go
+++ b/src/net/http/request.go
@@ -547,6 +547,23 @@ func ParseHTTPVersion(vers string) (major, minor int, ok bool) {
 	return major, minor, true
 }
 
+func validMethod(method string) bool {
+	/*
+	     Method         = "OPTIONS"                ; Section 9.2
+	                    | "GET"                    ; Section 9.3
+	                    | "HEAD"                   ; Section 9.4
+	                    | "POST"                   ; Section 9.5
+	                    | "PUT"                    ; Section 9.6
+	                    | "DELETE"                 ; Section 9.7
+	                    | "TRACE"                  ; Section 9.8
+	                    | "CONNECT"                ; Section 9.9
+	                    | extension-method
+	   extension-method = token
+	     token          = 1*<any CHAR except CTLs or separators>
+	*/
+	return len(method) > 0 && strings.IndexFunc(method, isNotToken) == -1
+}
+
 // NewRequest returns a new Request given a method, URL, and optional body.
 //
 // If the provided body is also an io.Closer, the returned
@@ -560,6 +577,9 @@ func ParseHTTPVersion(vers string) (major, minor int, ok bool) {
 // type's documentation for the difference between inbound and outbound
 // request fields.
 func NewRequest(method, urlStr string, body io.Reader) (*Request, error) {
+	if !validMethod(method) {
+		return nil, fmt.Errorf("net/http: invalid method %q", method)
+	}
 	u, err := url.Parse(urlStr)
 	if err != nil {
 		return nil, err
diff --git a/src/net/http/request_test.go b/src/net/http/request_test.go
index 627620c0c4..0ed68ed66a 100644
--- a/src/net/http/request_test.go
+++ b/src/net/http/request_test.go
@@ -355,6 +355,22 @@ func TestNewRequestHost(t *testing.T) {
 	}
 }
 
+func TestRequestInvalidMethod(t *testing.T) {
+	_, err := NewRequest("bad method", "http://foo.com/", nil)
+	if err == nil {
+		t.Error("expected error from NewRequest with invalid method")
+	}
+	req, err := NewRequest("GET", "http://foo.example/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req.Method = "bad method"
+	_, err = DefaultClient.Do(req)
+	if err == nil || !strings.Contains(err.Error(), "invalid method") {
+		t.Errorf("Transport error = %v; want invalid method", err)
+	}
+}
+
 func TestNewRequestContentLength(t *testing.T) {
 	readByte := func(r io.Reader) io.Reader {
 		var b [1]byte
diff --git a/src/net/http/transport.go b/src/net/http/transport.go
index 17a8d7b8a7..96096a6bef 100644
--- a/src/net/http/transport.go
+++ b/src/net/http/transport.go
@@ -237,6 +237,9 @@ func (t *Transport) RoundTrip(req *Request) (*Response, error) {
 		req.closeBody()
 		return nil, &badStringError{"unsupported protocol scheme", s}
 	}
+	if !validMethod(req.Method) {
+		return nil, fmt.Errorf("net/http: invalid method %q", req.Method)
+	}
 	if req.URL.Host == "" {
 		req.closeBody()
 		return nil, errors.New("http: no Host in request URL")
diff --git a/src/net/http/transport_test.go b/src/net/http/transport_test.go
index f721fd5558..a404eeb5cc 100644
--- a/src/net/http/transport_test.go
+++ b/src/net/http/transport_test.go
@@ -1775,6 +1775,7 @@ func TestTransportNoHost(t *testing.T) {
 	defer afterTest(t)
 	tr := &Transport{}
 	_, err := tr.RoundTrip(&Request{
+		Method: "GET",
 		Header: make(Header),
 		URL: &url.URL{
 			Scheme: "http",