diff --git a/test-server/test-client.c b/test-server/test-client.c
index debd43a..b602442 100644
--- a/test-server/test-client.c
+++ b/test-server/test-client.c
@@ -150,9 +150,16 @@
 					(int)random() % 250,
 					(int)random() % 24);
 
-		libwebsocket_write(wsi,
+		n = libwebsocket_write(wsi,
 		   &buf[LWS_SEND_BUFFER_PRE_PADDING], l, opts | LWS_WRITE_TEXT);
 
+		if (n < 0)
+			return -1;
+		if (n < l) {
+			lwsl_err("Partial write LWS_CALLBACK_CLIENT_WRITEABLE\n");
+			return -1;
+		}
+
 		mirror_lifetime--;
 		if (!mirror_lifetime) {
 			fprintf(stderr, "closing mirror session\n");