diff --git a/composer.json b/composer.json
index 619920a78..4f4d8af27 100644
--- a/composer.json
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diff --git a/composer.lock b/composer.lock
index f39545b62..e0b727b02 100644
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-                "ruflin/elastica": "Allow sending log messages to an Elastic Search server"
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@@ -1533,6 +1533,68 @@
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@@ -2315,6 +2377,57 @@
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             ],
             "description": "Symfony Translation Component",
             "homepage": "https://symfony.com",
-            "time": "2016-06-06 11:33:26"
+            "time": "2016-06-29 05:40:00"
         },
         {
             "name": "symfony/validator",
-            "version": "v2.8.7",
+            "version": "v2.8.8",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/validator.git",
-                "reference": "4c8f9fd8e2150dbc4745ef13378e690588365df0"
+                "reference": "366674c28bf7a107a8bce280c668bac40aeb090e"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/validator/zipball/4c8f9fd8e2150dbc4745ef13378e690588365df0",
-                "reference": "4c8f9fd8e2150dbc4745ef13378e690588365df0",
+                "url": "https://api.github.com/repos/symfony/validator/zipball/366674c28bf7a107a8bce280c668bac40aeb090e",
+                "reference": "366674c28bf7a107a8bce280c668bac40aeb090e",
                 "shasum": ""
             },
             "require": {
@@ -3012,29 +3125,29 @@
             ],
             "description": "Symfony Validator Component",
             "homepage": "https://symfony.com",
-            "time": "2016-04-14 08:48:44"
+            "time": "2016-06-29 05:29:29"
         },
         {
             "name": "symfony/yaml",
-            "version": "v2.8.7",
+            "version": "v3.1.2",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/yaml.git",
-                "reference": "815fabf3f48c7d1df345a69d1ad1a88f59757b34"
+                "reference": "2884c26ce4c1d61aebf423a8b912950fe7c764de"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/yaml/zipball/815fabf3f48c7d1df345a69d1ad1a88f59757b34",
-                "reference": "815fabf3f48c7d1df345a69d1ad1a88f59757b34",
+                "url": "https://api.github.com/repos/symfony/yaml/zipball/2884c26ce4c1d61aebf423a8b912950fe7c764de",
+                "reference": "2884c26ce4c1d61aebf423a8b912950fe7c764de",
                 "shasum": ""
             },
             "require": {
-                "php": ">=5.3.9"
+                "php": ">=5.5.9"
             },
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "2.8-dev"
+                    "dev-master": "3.1-dev"
                 }
             },
             "autoload": {
@@ -3061,7 +3174,7 @@
             ],
             "description": "Symfony Yaml Component",
             "homepage": "https://symfony.com",
-            "time": "2016-06-06 11:11:27"
+            "time": "2016-06-29 05:41:56"
         },
         {
             "name": "twig/twig",
diff --git a/src/LaunchDarkly/LDClient.php b/src/LaunchDarkly/LDClient.php
index a2d8c14af..d93491361 100644
--- a/src/LaunchDarkly/LDClient.php
+++ b/src/LaunchDarkly/LDClient.php
@@ -64,6 +64,10 @@ public function __construct($apiKey, $options = array()) {
         } else {
             $featureRequesterClass = '\\LaunchDarkly\\GuzzleFeatureRequester';
         }
+
+        if (!is_a($featureRequesterClass, FeatureRequester::class, true)) {
+            throw new \InvalidArgumentException;
+        }
         $this->_featureRequester = new $featureRequesterClass($this->_baseUri, $apiKey, $options);
     }
 
diff --git a/tests/LDClientTest.php b/tests/LDClientTest.php
index 56b7da442..42f86ee06 100644
--- a/tests/LDClientTest.php
+++ b/tests/LDClientTest.php
@@ -1,6 +1,7 @@
 <?php
 namespace LaunchDarkly\Tests;
 
+use InvalidArgumentException;
 use LaunchDarkly\FeatureRequester;
 use LaunchDarkly\LDClient;
 use LaunchDarkly\LDUserBuilder;
@@ -66,6 +67,11 @@ public function testToggleEventsOff() {
         $queue = getPrivateField($proc, '_queue');
         $this->assertEquals(0, sizeof($queue));
     }
+
+    public function testOnlyValidFeatureRequester() {
+        $this->setExpectedException(InvalidArgumentException::class);
+        new LDClient("BOGUS_API_KEY", ['feature_requester_class' => 'stdClass']);
+    }
 }