diff --git a/modules/servers/oauth2-proxy.nix b/modules/servers/oauth2-proxy.nix
index 33c8511..21b33c6 100644
--- a/modules/servers/oauth2-proxy.nix
+++ b/modules/servers/oauth2-proxy.nix
@@ -44,6 +44,7 @@ in
         auth-logging = true;
         session-store-type = "cookie";
         skip-provider-button = true;
+        code-challenge-method = "S256";
       };
     };
   };