diff --git a/composer.json b/composer.json
index 73cf14314..2e2bbb148 100644
--- a/composer.json
+++ b/composer.json
@@ -130,10 +130,10 @@
             "php var/box.phar compile"
         ],
         "mutation": [
-            "infection --threads=4 --only-covered"
+            "infection --threads=2 --only-covered"
         ],
         "mutation-diff-lines": [
-            "infection --threads=4 --only-covered --git-diff-lines --git-diff-base=origin/$GITHUB_BASE_REF --min-covered-msi=100"
+            "infection --threads=2 --only-covered --git-diff-lines --git-diff-base=origin/$GITHUB_BASE_REF --min-covered-msi=100"
         ],
         "cs": "phpcs",
         "cbf": "phpcbf",