diff --git a/.gitignore b/.gitignore
index 53724108..d50b31d2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -45,6 +45,7 @@
 /mkinstalldirs
 /modules/
 /package.xml
+/composer.phar
 /phpunit.result.cache
 /run-tests.php
 /src/.idea/
diff --git a/Couchbase/Cluster.php b/Couchbase/Cluster.php
index e63aa776..19bfc882 100644
--- a/Couchbase/Cluster.php
+++ b/Couchbase/Cluster.php
@@ -85,8 +85,17 @@ public static function connect(string $connectionString, ClusterOptions $options
         return ClusterRegistry::connect($connectionString, $options);
     }
 
+    /**
+     * @throws InvalidArgumentException if runtime dependencies are missing ("protobuf" and "grpc" modules)
+     */
     private static function enableProtostellar(): void
     {
+        if (!extension_loaded("protobuf")) {
+            throw new InvalidArgumentException("couchbase2:// protocol requires protobuf extension");
+        }
+        if (!extension_loaded("grpc")) {
+            throw new InvalidArgumentException("couchbase2:// protocol requires grpc extension");
+        }
         ClusterRegistry::registerConnectionHandler(
             "/^protostellar:\/\//",
             function (string $connectionString, ClusterOptions $options) {
diff --git a/composer.json b/composer.json
index f8ca88bf..2640f305 100644
--- a/composer.json
+++ b/composer.json
@@ -16,14 +16,16 @@
       "email": "sergey.avseyev@gmail.com"
     }
   ],
-  "require": {
-    "ext-json": "*",
+  "suggest": {
     "ext-grpc": "^1.15",
     "ext-protobuf": "^3.21",
     "google/protobuf": "^3.21",
     "grpc/grpc": "^1.42",
     "google/common-protos": "^3.1"
   },
+  "require": {
+    "ext-json": "*"
+  },
   "require-dev": {
     "ext-sockets": "*",
     "phpunit/phpunit": "^9"