diff --git a/README.md b/README.md
index ad510f1..11dc608 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ A PHP API client for the SEMrush API.
 ## Supported actions:
 
 * domain_ranks
-* domain_domain
+* domain_domains
 * domain_rank
 * domain_rank_history
 * domain_organic
diff --git a/src/Model/Request.php b/src/Model/Request.php
index 121e81b..124b52d 100644
--- a/src/Model/Request.php
+++ b/src/Model/Request.php
@@ -228,20 +228,26 @@ protected function validateDomain($key, $domain)
      * @param string $key
      * @param string $domain
      * @throws InvalidOptionException
+     *
+     * Validates the format <sign>|<type>|<domain>|<sign>|<type>|<domain>|...
      */
     protected function validateDomains($key, $domains)
     {
         $parts = explode('|', $domains);
 
+        if (count($parts) > 5 * 3) { // 5 domains max, each with 3 parts
+            throw new InvalidOptionException("[{$key}] contains too many domains");
+        }
+
         for ($i = 0; $i < count($parts); $i++) {
            switch ($i % 3) {
                case 0:
-                   if (!in_array($parts[$i], ['+', '-', '/', '*'])) {
+                   if (!in_array($parts[$i], ['+', '-', '/', '*'], true)) {
                        throw new InvalidOptionException("[{$key}] contains an invalid sign [{ $parts[$i]}]");
                    }
                    break;
                case 1:
-                   if (!in_array($parts[$i], ['or', 'ad'])) {
+                   if (!in_array($parts[$i], ['or', 'ad'], true)) {
                        throw new InvalidOptionException("[{$key}] contains an invalid type - must be or or ad [{ $parts[$i]}]");
                    }
                     break;