diff --git a/Common/Http/Psr/Client/Discovery/Guzzle.php b/Common/Http/Psr/Client/Discovery/Guzzle.php
index 8d013c9..d873674 100644
--- a/Common/Http/Psr/Client/Discovery/Guzzle.php
+++ b/Common/Http/Psr/Client/Discovery/Guzzle.php
@@ -11,7 +11,7 @@ class Guzzle implements DiscoveryInterface
 {
     public function available(): bool
     {
-        return class_exists(Client::class);
+        return class_exists(Client::class) && is_a(Client::class, ClientInterface::class, true);
     }
 
     public function create(mixed $options): ClientInterface
diff --git a/Trace/AutoRootSpan.php b/Trace/AutoRootSpan.php
index ed4f6eb..69790cd 100644
--- a/Trace/AutoRootSpan.php
+++ b/Trace/AutoRootSpan.php
@@ -8,6 +8,7 @@
 use Http\Discovery\Psr17FactoryDiscovery;
 use Nyholm\Psr7Server\ServerRequestCreator;
 use OpenTelemetry\API\Behavior\LogsMessagesTrait;
+use OpenTelemetry\API\Common\Time\ClockInterface;
 use OpenTelemetry\API\Globals;
 use OpenTelemetry\API\Trace\Span;
 use OpenTelemetry\API\Trace\SpanKind;
@@ -47,7 +48,7 @@ public static function create(ServerRequestInterface $request): void
             : (int) microtime(true);
         $span = $tracer->spanBuilder($request->getMethod())
             ->setSpanKind(SpanKind::KIND_SERVER)
-            ->setStartTimestamp((int) ($startTime*1_000_000))
+            ->setStartTimestamp((int) ($startTime*ClockInterface::NANOS_PER_SECOND))
             ->setParent($parent)
             ->setAttribute(TraceAttributes::URL_FULL, (string) $request->getUri())
             ->setAttribute(TraceAttributes::HTTP_REQUEST_METHOD, $request->getMethod())