diff --git a/CONFLICTS.md b/CONFLICTS.md
new file mode 100644
index 00000000..b62f9c57
--- /dev/null
+++ b/CONFLICTS.md
@@ -0,0 +1,17 @@
+# Conflicts
+
+This document explains why certain conflicts were added to `composer.json` and references related issues.
+
+## twig/twig 3.29.0
+
+**Added:** 2026-09-21
+
+**Reason:** Twig 3.29.0 changed `TemplateWrapper::unwrap()` to require an
+`Environment $env` argument (twigphp/Twig#4935). `symfony/twig-bridge`'s
+`TwigRendererEngine` still calls it with no arguments when loading form
+themes, so every form render throws `ArgumentCountError`. `sylius/mailer-bundle`
+had the same call in `EmailTwigAdapter`. The BC break is reverted in the next
+Twig release (twigphp/Twig#4936), so only 3.29.0 is affected.
+
+**Remove when:** Twig 3.29.0 is no longer worth guarding against (the fix ships
+in the next Twig release, see twigphp/Twig#4936).
diff --git a/composer.json b/composer.json
index 68965f7d..8471d84e 100644
--- a/composer.json
+++ b/composer.json
@@ -113,6 +113,9 @@
             "require": "8.0.*"
         }
     },
+    "conflict": {
+        "twig/twig": "3.29.0"
+    },
     "scripts": {
         "auto-scripts": {
             "cache:clear": "symfony-cmd",