diff --git a/.arcconfig b/.arcconfig
--- a/.arcconfig
+++ b/.arcconfig
@@ -1,5 +1,4 @@
 {
   "phabricator.uri": "https://secure.phabricator.com/",
-  "unit.engine": "PhutilUnitTestEngine",
   "load": ["src/"]
 }
diff --git a/.arcunit b/.arcunit
new file mode 100644
--- /dev/null
+++ b/.arcunit
@@ -0,0 +1,8 @@
+{
+  "engines": {
+    "phutil": {
+      "type": "phutil",
+      "include": "(\\.php$)"
+    }
+  }
+}