diff --git a/Messerli.Session.AspNetCore/Internal/Response.cs b/Messerli.Session.AspNetCore/Internal/Response.cs
index b5be5e0..cdfb0b6 100644
--- a/Messerli.Session.AspNetCore/Internal/Response.cs
+++ b/Messerli.Session.AspNetCore/Internal/Response.cs
@@ -44,7 +44,9 @@ public void SetHeader(string name, string value)
             => _httpContext.Response.Headers.Append(name, value);
 
         public string? GetFirstHeaderValue(string name)
-            => _httpContext.Response.Headers[name].FirstOrDefault();
+            => _httpContext.Response.Headers.TryGetValue(name, out var value)
+                ? value.FirstOrDefault()
+                : null;
 
         private bool MapSecurePreferenceToBool(CookieSecurePreference securePreference)
             => securePreference switch