diff --git a/src/Controller/GraphController.php b/src/Controller/GraphController.php
index 455b980..6fbec66 100644
--- a/src/Controller/GraphController.php
+++ b/src/Controller/GraphController.php
@@ -2,11 +2,10 @@
 
 namespace App\Controller;
 
-use App\Service\ProviderInterface;
+use App\Service\ContributionAggregator;
 use App\Service\SvgRenderer;
 use Psr\Log\LoggerInterface;
 use Symfony\Component\DependencyInjection\Attribute\Autowire;
-use Symfony\Component\DependencyInjection\Attribute\TaggedIterator;
 use Symfony\Component\HttpFoundation\RedirectResponse;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
@@ -20,8 +19,7 @@ class GraphController
     private readonly array $allowedHosts;
 
     public function __construct(
-        #[TaggedIterator('app.provider')]
-        private readonly iterable $providers,
+        private readonly ContributionAggregator $aggregator,
         private readonly SvgRenderer $renderer,
         private readonly CacheInterface $cache,
         private readonly LoggerInterface $logger,
@@ -52,7 +50,7 @@ class GraphController
             $cacheMiss = true;
             $item->expiresAfter(3600);
 
-            return $this->renderer->render($this->fetchAllContributions(), $theme);
+            return $this->renderer->render($this->aggregator->aggregate(), $theme);
         });
 
         $this->logger->debug('GraphController: cache ' . ($cacheMiss ? 'miss' : 'hit'), ['theme' => $theme]);
@@ -78,34 +76,5 @@ class GraphController
         return new Response('{"status":"ok"}', 200, ['Content-Type' => 'application/json']);
     }
 
-    /** @return array<string, int> */
-    private function fetchAllContributions(): array
-    {
-        $contributions = [];
 
-        /** @var ProviderInterface $provider */
-        foreach ($this->providers as $provider) {
-            if (!$provider->isConfigured()) {
-                continue;
-            }
-
-            try {
-                $contributions = $this->merge($contributions, $provider->fetch());
-            } catch (\Throwable $e) {
-                $this->logger->warning(sprintf('%s fetch failed: %s', $provider::class, $e->getMessage()), ['exception' => $e]);
-            }
-        }
-
-        return $contributions;
-    }
-
-    /** @param array<string, int> $base @param array<string, int> $new @return array<string, int> */
-    private function merge(array $base, array $new): array
-    {
-        foreach ($new as $date => $count) {
-            $base[$date] = ($base[$date] ?? 0) + $count;
-        }
-
-        return $base;
-    }
 }
diff --git a/src/Service/ContributionAggregator.php b/src/Service/ContributionAggregator.php
new file mode 100644
index 0000000..370d05f
--- /dev/null
+++ b/src/Service/ContributionAggregator.php
@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service;
+
+use Psr\Log\LoggerInterface;
+use Symfony\Component\DependencyInjection\Attribute\AutowireIterator;
+
+final class ContributionAggregator
+{
+    public function __construct(
+        #[AutowireIterator('app.provider')]
+        private readonly iterable $providers,
+        private readonly LoggerInterface $logger,
+    ) {}
+
+    /** @return array<string, int> */
+    public function aggregate(): array
+    {
+        $contributions = [];
+
+        /** @var ProviderInterface $provider */
+        foreach ($this->providers as $provider) {
+            if (!$provider->isConfigured()) {
+                continue;
+            }
+
+            try {
+                foreach ($provider->fetch() as $date => $count) {
+                    $contributions[$date] = ($contributions[$date] ?? 0) + $count;
+                }
+            } catch (\Throwable $e) {
+                $this->logger->warning(sprintf('%s fetch failed: %s', $provider::class, $e->getMessage()), ['exception' => $e]);
+            }
+        }
+
+        return $contributions;
+    }
+}