diff --git a/lc0_main.go b/lc0_main.go
index b5a73e0..da5da6d 100644
--- a/lc0_main.go
+++ b/lc0_main.go
@@ -61,7 +61,7 @@ var (
 	backopts = flag.String("backend-opts", "",
 		`Options for the lc0 mux. backend. Example: --backend-opts="cudnn(gpu=1)"`)
 	parallel      = flag.Int("parallelism", -1, "Number of games to play in parallel (-1 for default)")
-	cacheDir      = flag.String("cache", "", "Directory to use for downloaded networks cache")
+	cacheDir      = flag.String("cache", "", "Directory to use for downloaded files cache (if it exists)")
 	useTestServer = flag.Bool("use-test-server", false, "Set host name to test server.")
 	runId         = flag.Uint("run", 0, "Which training run to contribute to (default 0 to let server decide)")
 	keep          = flag.Bool("keep", false, "Do not delete old network files")
@@ -133,7 +133,7 @@ func getExtraParams() map[string]string {
 	return map[string]string{
 		"user":       *user,
 		"password":   *password,
-		"version":    "28",
+		"version":    "29",
 		"token":      strconv.Itoa(randId),
 		"train_only": strconv.FormatBool(*trainOnly),
 		"hostname":   *localHost,
@@ -363,11 +363,11 @@ func (c *cmdWrapper) launch(networkPath string, otherNetPath string, args []stri
 		testedDxNet = networkPath
 	}
 	if *backopts != "" {
-		// Check against small token blacklist, currently only "random"
+		// Check against small token blacklist, currently only "mlh", "random" and "recordreplay"
 		tokens := regexp.MustCompile("[,=().0-9]").Split(*backopts, -1)
 		for _, token := range tokens {
 			switch token {
-			case "random":
+			case "mlh", "random", "recordreplay":
 				log.Fatalf("Not accepted in --backend-opts: %s", token)
 			}
 		}
@@ -815,12 +815,9 @@ func acquireLock(dir string, sha string) (lockfile.Lockfile, error) {
 	return lock, err
 }
 
-func getNetwork(httpClient *http.Client, sha string, keepTime string) (string, error) {
-	dir := "client-cache"
-	if len(*cacheDir) != 0 {
-		dir = *cacheDir
-	} else {
-		userCache := ""
+func makeCacheDir(dir string) string {
+	userCache := *cacheDir
+	if len(userCache) == 0 {
 		if runtime.GOOS == "linux" {
 			userCache = os.Getenv("XDG_CACHE_HOME")
 			if len(userCache) == 0 {
@@ -835,16 +832,22 @@ func getNetwork(httpClient *http.Client, sha string, keepTime string) (string, e
 				userCache = homeDir + "/Library/Caches"
 			}
 		}
-
-		if len(userCache) != 0 {
-			_, err := os.Stat(userCache)
-			if err == nil {
+	}
+	if len(userCache) != 0 {
+		_, err := os.Stat(userCache)
+		if err == nil {
+			if len(*cacheDir) == 0 {
 				userCache = filepath.Join(userCache, "lc0")
-				dir = filepath.Join(userCache, dir)
 			}
+			dir = filepath.Join(userCache, dir)
 		}
 	}
 	os.MkdirAll(dir, os.ModePerm)
+	return dir
+}
+
+func getNetwork(httpClient *http.Client, sha string, keepTime string) (string, error) {
+	dir := makeCacheDir("client-cache")
 	if keepTime != inf {
 		err := removeAllExcept(dir, sha, keepTime)
 		if err != nil {
@@ -880,9 +883,32 @@ func getNetwork(httpClient *http.Client, sha string, keepTime string) (string, e
 	return checkValidNetwork(dir, sha)
 }
 
-func getBook(httpClient *http.Client, book_url string) (string, error) {
-	dir := "books"
-	os.MkdirAll(dir, os.ModePerm)
+func checkValidBook(path string, sha string) (string, error) {
+	// File already exists?
+	_, err := os.Stat(path)
+	if err == nil {
+		file, _ := os.Open(path)
+		sum := sha256.New()
+		_, err := io.Copy(sum, file);
+		got := fmt.Sprintf("%x", sum.Sum(nil))
+		if sha != got {
+			text := fmt.Sprintf("book sha mismatch want:\n%s\ngot\n%s\n", sha, got)
+			err = errors.New(text)
+		}
+		file.Close()
+		if err != nil {
+			fmt.Printf("Deleting invalid book...\n")
+			os.Remove(path)
+			return path, err
+		} else {
+			return path, nil
+		}
+	}
+	return path, err
+}
+
+func getBook(httpClient *http.Client, book_url string, sha string) (string, error) {
+	dir := makeCacheDir("books")
 	u, err := url.Parse(book_url)
 	if err != nil {
 		log.Println("Unable to parse book URL")
@@ -891,7 +917,7 @@ func getBook(httpClient *http.Client, book_url string) (string, error) {
 	s := strings.Split(u.Path, "/")
 	book_name := s[len(s)-1]
 	path := filepath.Join(dir, book_name)
-	_, err = os.Stat(path)
+	_, err = checkValidBook(path, sha)
 	if err == nil {
 		// Book is there, use it.
 		return path, nil
@@ -934,7 +960,7 @@ func getBook(httpClient *http.Client, book_url string) (string, error) {
 	// Ensure tmpfile is erased
 	os.Remove(out.Name())
 
-	return path, err
+	return checkValidBook(path, sha)
 }
 
 func nextGame(httpClient *http.Client, count int) error {
@@ -958,10 +984,17 @@ func nextGame(httpClient *http.Client, count int) error {
 	log.Printf("serverParams: %s", serverParams)
 
 	if nextGame.BookUrl != "" {
-		_, err := getBook(&http.Client{}, nextGame.BookUrl)
+		book, err := getBook(&http.Client{}, nextGame.BookUrl, nextGame.BookSha)
 		if err != nil {
 			return err
 		}
+		// Replace the book file with the correct path
+		for i := range serverParams {
+			if strings.HasPrefix(serverParams[i], "--openings-pgn=") {
+				serverParams[i] = "--openings-pgn=" + book
+				break
+			}
+		}
 	}
 
 	if nextGame.Type == "match" {
diff --git a/src/client/client_http.go b/src/client/client_http.go
index 39b7723..b2bee1d 100644
--- a/src/client/client_http.go
+++ b/src/client/client_http.go
@@ -87,6 +87,7 @@ type NextGameResponse struct {
 	MatchGameId  uint
 	KeepTime     string
 	BookUrl      string
+	BookSha      string
 }
 
 func NextGame(httpClient *http.Client, hostname string, params map[string]string) (NextGameResponse, error) {