diff --git a/util/app.h b/util/app.h
index 8161419..1a96c22 100644
--- a/util/app.h
+++ b/util/app.h
@@ -80,8 +80,7 @@ class AppArgs : public ArgsBase<AppArgs> {
   void ChooseNumThreads() {
     if (num_threads == kDefaultNumThreads) {
       // This is a rough heuristic, replace with something better in the future.
-      num_threads = static_cast<size_t>(std::clamp(
-          static_cast<int>(std::thread::hardware_concurrency()) - 2, 1, 18));
+      num_threads = GetSupportedThreadCount();
     }
   }
 
@@ -91,6 +90,11 @@ class AppArgs : public ArgsBase<AppArgs> {
     ChooseNumThreads();
   }
 
+  static inline size_t GetSupportedThreadCount() {
+    return static_cast<size_t>(std::clamp(
+        static_cast<int>(std::thread::hardware_concurrency()) - 2, 1, 18));
+  }
+
   Path log;  // output
   int verbosity;
   size_t num_threads;