diff --git a/http2/transport_test.go b/http2/transport_test.go
index 23b4989..ec7493c 100644
--- a/http2/transport_test.go
+++ b/http2/transport_test.go
@@ -3385,6 +3385,10 @@
 
 	ct.client = func() error {
 		defer ct.cc.(*net.TCPConn).CloseWrite()
+		if runtime.GOOS == "plan9" {
+			// CloseWrite not supported on Plan 9; Issue 17906
+			defer ct.cc.(*net.TCPConn).Close()
+		}
 		defer close(clientDone)
 		req, _ := http.NewRequest("GET", "https://dummy.tld/", nil)
 		res, err := ct.tr.RoundTrip(req)