diff --git a/libsrc/include/mystdlib.h b/libsrc/include/mystdlib.h
index a3a9103a..e72b6a85 100644
--- a/libsrc/include/mystdlib.h
+++ b/libsrc/include/mystdlib.h
@@ -31,6 +31,7 @@
 // #undef SEEK_CUR
 // #undef SEEK_END
 #include <mpi.h>
+#include <unistd.h>  // for usleep (only for parallel)
 #endif
 
 #ifdef _OPENMP