diff --git a/src/util/u_cpu_detect.c b/src/util/u_cpu_detect.c
index 636c186743c..87f47cda931 100644
--- a/src/util/u_cpu_detect.c
+++ b/src/util/u_cpu_detect.c
@@ -625,7 +625,7 @@ util_cpu_detect_once(void)
    if (available_cpus == 0) {
       const int mib[] = { CTL_HW, HW_NCPUONLINE };
       int ncpu;
-      int len = sizeof(ncpu);
+      size_t len = sizeof(ncpu);
 
       sysctl(mib, 2, &ncpu, &len, NULL, 0);
       available_cpus = ncpu;