diff --git a/src/net/http/transport.go b/src/net/http/transport.go
index 44d5515705..bbac2bf448 100644
--- a/src/net/http/transport.go
+++ b/src/net/http/transport.go
@@ -513,6 +513,22 @@ func (t *Transport) alternateRoundTripper(req *Request) RoundTripper {
 	return altProto[req.URL.Scheme]
 }
 
+func validateHeaders(hdrs Header) string {
+	for k, vv := range hdrs {
+		if !httpguts.ValidHeaderFieldName(k) {
+			return fmt.Sprintf("field name %q", k)
+		}
+		for _, v := range vv {
+			if !httpguts.ValidHeaderFieldValue(v) {
+				// Don't include the value in the error,
+				// because it may be sensitive.
+				return fmt.Sprintf("field value for %q", k)
+			}
+		}
+	}
+	return ""
+}
+
 // roundTrip implements a RoundTripper over HTTP.
 func (t *Transport) roundTrip(req *Request) (*Response, error) {
 	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
@@ -530,18 +546,16 @@ func (t *Transport) roundTrip(req *Request) (*Response, error) {
 	scheme := req.URL.Scheme
 	isHTTP := scheme == "http" || scheme == "https"
 	if isHTTP {
-		for k, vv := range req.Header {
-			if !httpguts.ValidHeaderFieldName(k) {
-				req.closeBody()
-				return nil, fmt.Errorf("net/http: invalid header field name %q", k)
-			}
-			for _, v := range vv {
-				if !httpguts.ValidHeaderFieldValue(v) {
-					req.closeBody()
-					// Don't include the value in the error, because it may be sensitive.
-					return nil, fmt.Errorf("net/http: invalid header field value for %q", k)
-				}
-			}
+		// Validate the outgoing headers.
+		if err := validateHeaders(req.Header); err != "" {
+			req.closeBody()
+			return nil, fmt.Errorf("net/http: invalid header %s", err)
+		}
+
+		// Validate the outgoing trailers too.
+		if err := validateHeaders(req.Trailer); err != "" {
+			req.closeBody()
+			return nil, fmt.Errorf("net/http: invalid trailer %s", err)
 		}
 	}
 
diff --git a/src/net/http/transport_test.go b/src/net/http/transport_test.go
index d3f43cfd9a..204133f130 100644
--- a/src/net/http/transport_test.go
+++ b/src/net/http/transport_test.go
@@ -7031,3 +7031,42 @@ func TestTransportReqCancelerCleanupOnRequestBodyWriteError(t *testing.T) {
 		return true
 	})
 }
+
+func TestValidateClientRequestTrailers(t *testing.T) {
+	run(t, testValidateClientRequestTrailers)
+}
+
+func testValidateClientRequestTrailers(t *testing.T, mode testMode) {
+	cst := newClientServerTest(t, mode, HandlerFunc(func(rw ResponseWriter, req *Request) {
+		rw.Write([]byte("Hello"))
+	})).ts
+
+	cases := []struct {
+		trailer Header
+		wantErr string
+	}{
+		{Header{"Trx": {"x\r\nX-Another-One"}}, `invalid trailer field value for "Trx"`},
+		{Header{"\r\nTrx": {"X-Another-One"}}, `invalid trailer field name "\r\nTrx"`},
+	}
+
+	for i, tt := range cases {
+		testName := fmt.Sprintf("%s%d", mode, i)
+		t.Run(testName, func(t *testing.T) {
+			req, err := NewRequest("GET", cst.URL, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			req.Trailer = tt.trailer
+			res, err := cst.Client().Do(req)
+			if err == nil {
+				t.Fatal("Expected an error")
+			}
+			if g, w := err.Error(), tt.wantErr; !strings.Contains(g, w) {
+				t.Fatalf("Mismatched error\n\t%q\ndoes not contain\n\t%q", g, w)
+			}
+			if res != nil {
+				t.Fatal("Unexpected non-nil response")
+			}
+		})
+	}
+}