diff --git a/src/Http/HttpMessageHelper.php b/src/Http/HttpMessageHelper.php
new file mode 100644
index 0000000..92ddf4e
--- /dev/null
+++ b/src/Http/HttpMessageHelper.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the worldia/instrumentation-bundle package.
+ * (c) Worldia <developers@worldia.com>
+ */
+
+namespace Instrumentation\Http;
+
+class HttpMessageHelper
+{
+    /**
+     * @param array<string,string[]> $headers
+     */
+    public static function formatHeadersForSpanAttribute(array $headers): string
+    {
+        $lines = [];
+        foreach ($headers as $name => $values) {
+            foreach ($values as $value) {
+                $lines[] = sprintf('%s: %s', mb_strtolower($name), $value);
+            }
+        }
+
+        return implode(\PHP_EOL, $lines);
+    }
+}
diff --git a/src/Http/TracedResponse.php b/src/Http/TracedResponse.php
index 988768f..8a6a1de 100644
--- a/src/Http/TracedResponse.php
+++ b/src/Http/TracedResponse.php
@@ -182,13 +182,7 @@ protected function endTracing(): void
 
         try {
             if (\in_array('response.headers', $info['user_data']['span_attributes'] ?? [])) {
-                $headers = [];
-                $raw = $this->getHeaders(false);
-                foreach ($raw as $header => $value) {
-                    $headers[$header] = $this->toReadableHeaderValue($value);
-                }
-
-                $this->span->setAttribute('response.headers', $headers);
+                $this->span->setAttribute('response.headers', HttpMessageHelper::formatHeadersForSpanAttribute($this->getHeaders(false)));
             }
 
             if (\in_array('response.body', $info['user_data']['span_attributes'] ?? [])) {
diff --git a/src/Http/TracingHttpClient.php b/src/Http/TracingHttpClient.php
index 6da6f49..5cda904 100644
--- a/src/Http/TracingHttpClient.php
+++ b/src/Http/TracingHttpClient.php
@@ -93,6 +93,9 @@ public function request(string $method, string $url, array $options = []): Respo
             if (\in_array('request.body', $options['user_data']['span_attributes'])) {
                 $attributes['request.body'] = self::getRequestBody($options);
             }
+            if (\in_array('request.headers', $options['user_data']['span_attributes'])) {
+                $attributes['request.headers'] = HttpMessageHelper::formatHeadersForSpanAttribute($headers);
+            }
         } catch (\Throwable) {
         }