diff --git a/Build/build-reject-domainset.js b/Build/build-reject-domainset.js
index ceb6fae6..bf3ea1cf 100644
--- a/Build/build-reject-domainset.js
+++ b/Build/build-reject-domainset.js
@@ -2,7 +2,9 @@ const { promises: fsPromises } = require('fs');
 const { resolve: pathResolve } = require('path');
 const Piscina = require('piscina');
 const { processHosts, processFilterRules } = require('./lib/parse-filter');
-const threads = require('os').cpus().length - 1;
+const cpuCount = require('os').cpus().length;
+const { isCI } = require('ci-info');
+const threads = isCI ? cpuCount : cpuCount / 2;
 
 (async () => {
   /** @type Set<string> */
diff --git a/package.json b/package.json
index c4aa2271..6c5c4558 100644
--- a/package.json
+++ b/package.json
@@ -57,10 +57,11 @@
   "license": "ISC",
   "dependencies": {
     "@sukka/listdir": "^0.2.0",
+    "ci-info": "^3.3.2",
     "picocolors": "^1.0.0",
     "piscina": "^3.2.0",
     "table": "^6.8.0",
-    "undici": "^5.9.1"
+    "undici": "5.10.0"
   },
   "devDependencies": {
     "wireit": "^0.7.1"
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 5d7fab35..359d48a0 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -2,18 +2,20 @@ lockfileVersion: 5.4
 
 specifiers:
   '@sukka/listdir': ^0.2.0
+  ci-info: ^3.3.2
   picocolors: ^1.0.0
   piscina: ^3.2.0
   table: ^6.8.0
-  undici: ^5.9.1
+  undici: 5.10.0
   wireit: ^0.7.1
 
 dependencies:
   '@sukka/listdir': 0.2.0
+  ci-info: 3.3.2
   picocolors: 1.0.0
   piscina: 3.2.0
   table: 6.8.0
-  undici: 5.9.1
+  undici: 5.10.0
 
 devDependencies:
   wireit: 0.7.1
@@ -114,6 +116,10 @@ packages:
       fsevents: 2.3.2
     dev: true
 
+  /ci-info/3.3.2:
+    resolution: {integrity: sha512-xmDt/QIAdeZ9+nfdPsaBCpMvHNLFiLdjj59qjqn+6iPe6YmHGQ35sBnQ8uslRBXFmXkiZQOJRjvQeoGppoTjjg==}
+    dev: false
+
   /color-convert/2.0.1:
     resolution: {integrity: sha512-RRECPsj7iu/xb5oKYcsFHSppFNnsj/52OVTRKb4zP5onXwVF3zVmmToNcOfGC+CRDpfK/U584fMg38ZHCaElKQ==}
     engines: {node: '>=7.0.0'}
@@ -387,8 +393,8 @@ packages:
       is-number: 7.0.0
     dev: true
 
-  /undici/5.9.1:
-    resolution: {integrity: sha512-6fB3a+SNnWEm4CJbgo0/CWR8RGcOCQP68SF4X0mxtYTq2VNN8T88NYrWVBAeSX+zb7bny2dx2iYhP3XHi00omg==}
+  /undici/5.10.0:
+    resolution: {integrity: sha512-c8HsD3IbwmjjbLvoZuRI26TZic+TSEe8FPMLLOkN1AfYRhdjnKBU6yL+IwcSCbdZiX4e5t0lfMDLDCqj4Sq70g==}
     engines: {node: '>=12.18'}
     dev: false