diff --git a/composer.json b/composer.json
index 68a8137..ed99523 100644
--- a/composer.json
+++ b/composer.json
@@ -46,9 +46,7 @@
         ]
     },
     "require-dev": {
+        "psr/simple-cache": "^1 || ^2 || ^3",
         "symfony/event-dispatcher-contracts": "^1 || ^2 || ^3"
-    },
-    "conflict": {
-      "symfony/cache": ">=6"
     }
 }
diff --git a/composer.json.md b/composer.json.md
deleted file mode 100644
index 31e3dc5..0000000
--- a/composer.json.md
+++ /dev/null
@@ -1,10 +0,0 @@
-# Notes for comments.json
-
-Because comments are not allowed in JSON this file is used.
-
-`"symfony/cache": ">=6"` is part of the conflict section to avoid this error:
-
-> PHP Fatal error:  Declaration of Symfony\Component\Cache\CacheItem::expiresAt(?DateTimeInterface $expiration): Symfony\Component\ErrorHandler\DebugClassLoader
-> must be compatible with Psr\Cache\CacheItemInterface::expiresAt($expiration)
-
-The code of this extension itself doesn't require `symfony/cache`.
\ No newline at end of file
diff --git a/tests/docker-prepare.sh b/tests/docker-prepare.sh
index 3b83b0e..2eea5cf 100755
--- a/tests/docker-prepare.sh
+++ b/tests/docker-prepare.sh
@@ -40,5 +40,8 @@ else
 fi
 
 cd "$EXT_DIR"
+# In the container used for tests there seems to be psr/cache 1 installed somewhere.
+# This conflicts with symfony/cache >=6, thus we use version 5 here.
+composer require --no-update 'symfony/cache:^5'
 composer update --no-progress --prefer-dist --optimize-autoloader --no-dev
 composer composer-phpunit -- update --no-progress --prefer-dist