Index: src/sort.c
===================================================================
--- src/sort.c.orig
+++ src/sort.c
@@ -5291,7 +5291,11 @@ main (int argc, char **argv)
     {
       if (!nthreads)
         {
-          unsigned long int np = num_processors (NPROC_CURRENT_OVERRIDABLE);
+          unsigned long int np;
+          if (getenv("OMP_NUM_THREADS"))
+            np = num_processors (NPROC_CURRENT_OVERRIDABLE);
+          else
+            np = 1;
           nthreads = MIN (np, DEFAULT_MAX_THREADS);
         }