diff --git a/bin/ruby-build b/bin/ruby-build
index e82196b5..82e1b82f 100755
--- a/bin/ruby-build
+++ b/bin/ruby-build
@@ -154,7 +154,8 @@ num_cpu_cores() {
     num="$(sysctl -n hw.ncpu 2>/dev/null || true)"
     ;;
   * )
-    num="$(grep ^processor /proc/cpuinfo 2>/dev/null | wc -l | xargs)"
+    num="$({ getconf _NPROCESSORS_ONLN ||
+             grep -c ^processor /proc/cpuinfo; } 2>/dev/null)"
     num="${num#0}"
     ;;
   esac