diff --git a/src/ServerSocket.php b/src/ServerSocket.php
index 5ca035b..829cd53 100644
--- a/src/ServerSocket.php
+++ b/src/ServerSocket.php
@@ -13,6 +13,15 @@ public function enableCrypto(): Promise {
             return new Failure(new ClosedException("The socket has been closed"));
         }
 
+        $ctx = \stream_context_get_options($resource);
+        if (empty($ctx['ssl'])) {
+            return new Failure(new SocketException(
+                "Can't enable TLS without configuration. " .
+                "If you used Amp\\Socket\\listen(), be sure to pass a ServerTlsContext as third argument, " .
+                "otherwise set the 'ssl' context option to the PHP stream resource."
+            ));
+        }
+
         return Internal\enableCrypto($resource, [], true);
     }
 }