diff --git a/src/sigar.c b/src/sigar.c
index 285e6493..c0e9cb49 100644
--- a/src/sigar.c
+++ b/src/sigar.c
@@ -39,8 +39,8 @@ SIGAR_DECLARE(int) sigar_open(sigar_t **sigar)
     int status = sigar_os_open(sigar);
 
     if (status == SIGAR_OK) {
-        /* XXX tmp hack */
-        (*sigar)->cpu_list_cores = getenv("SIGAR_CPU_CORES") ? 1 : 0;
+        /* use env to revert to old behavior */
+        (*sigar)->cpu_list_cores = getenv("SIGAR_CPU_LIST_SOCKETS") ? 0 : 1;
         (*sigar)->pid = 0;
         (*sigar)->ifconf_buf = NULL;
         (*sigar)->ifconf_len = 0;