diff --git a/src/Client.php b/src/Client.php
index 422621b..89c245d 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -302,6 +302,10 @@ protected function configure(array $options): void
      */
     public function waitForData(float $maxSeconds): ?bool
     {
+        if (!$this->isConnected()) {
+            return null;
+        }
+
         return $this->socket->waitForData($maxSeconds);
     }
 }
diff --git a/src/Socket/AbstractSocket.php b/src/Socket/AbstractSocket.php
index b58b922..8904321 100644
--- a/src/Socket/AbstractSocket.php
+++ b/src/Socket/AbstractSocket.php
@@ -233,6 +233,10 @@ public function send(string $data): ?int
      */
     public function waitForData(float $maxSeconds): ?bool
     {
+        if (null === $this->socket) {
+            return null;
+        }
+
         $read = [$this->socket];
         $write = null;
         $except = null;
diff --git a/tests/ClientTest.php b/tests/ClientTest.php
index fe95f8f..d153bf4 100644
--- a/tests/ClientTest.php
+++ b/tests/ClientTest.php
@@ -89,6 +89,7 @@ public function testSend(): void
             $instance->addRequestHeader('X-Test', 'Custom Request Header');
 
             self::assertNull($instance->receive(), 'Receive before connect');
+            self::assertNull($instance->waitForData(0), 'Wait for data before connect');
 
             $success = $instance->connect();
             self::assertTrue($success, 'Client can connect to test server');
@@ -123,6 +124,7 @@ public function testSend(): void
             $instance->disconnect();
 
             self::assertFalse($instance->isConnected());
+            self::assertNull($instance->waitForData(0), 'Wait for data after disconnect');
         } finally {
             $helper->tearDown();
         }
diff --git a/tests/Socket/ClientSocketTest.php b/tests/Socket/ClientSocketTest.php
index f631a2e..3c1170d 100644
--- a/tests/Socket/ClientSocketTest.php
+++ b/tests/Socket/ClientSocketTest.php
@@ -110,6 +110,13 @@ public function testSendTooEarly(): void
         $instance->send('foo');
     }
 
+    public function testWaitForDataTooEarly(): void
+    {
+        $instance = self::getInstance('ws://localhost:8000');
+
+        self::assertNull($instance->waitForData(0));
+    }
+
     /**
      * Test the connect, send, receive method.
      */