From 6ed5f8094097a7a80456968142534bc5284bc73f Mon Sep 17 00:00:00 2001
From: Jonathan Keane <jkeane@gmail.com>
Date: Mon, 1 Dec 2025 14:11:20 -0600
Subject: [PATCH] respect makeflags if set

---
 r/tools/nixlibs.R | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/r/tools/nixlibs.R b/r/tools/nixlibs.R
index ee782bdeeac9..cace64b8e9f0 100644
--- a/r/tools/nixlibs.R
+++ b/r/tools/nixlibs.R
@@ -540,6 +540,12 @@ build_libarrow <- function(src_dir, dst_dir) {
   if (makeflags == "") {
     makeflags <- sprintf("-j%s", ncores)
     Sys.setenv(MAKEFLAGS = makeflags)
+  } else {
+    # Extract -j value from existing MAKEFLAGS if present
+    j_match <- regmatches(makeflags, regexpr("-j\\s*([0-9]+)", makeflags, perl = TRUE))
+    if (length(j_match) > 0) {
+      ncores <- as.integer(sub("-j\\s*", "", j_match, perl = TRUE))
+    }
   }
   if (!quietly) {
     lg("Building with MAKEFLAGS=%s", makeflags)