diff --git a/Carpet/CarpetLib/src/dist.cc b/Carpet/CarpetLib/src/dist.cc
index c870990..2e8edba 100644
--- a/Carpet/CarpetLib/src/dist.cc
+++ b/Carpet/CarpetLib/src/dist.cc
@@ -1,4 +1,5 @@
 #include <cassert>
+#include <cstdlib>
 
 #include <mpi.h>
 #ifdef _OPENMP
@@ -95,6 +96,11 @@ namespace dist {
       // Set number of threads which should be used
       // TODO: do this at startup, not in this routine
       omp_set_num_threads (num_threads);
+    } else if (num_threads == -2) {
+      if (not getenv ("OMP_NUM_THREADS")) {
+        // use only one thread of OMP_NUM_THREADS is not set
+        omp_set_num_threads (1);
+      }
     }
 #else
     if (num_threads > 0 and num_threads != 1) {