diff --git a/src/Makefile.MESONH.mk b/src/Makefile.MESONH.mk
index e411796b903d7662bbbe0be4647f8dddf079f065..5e3775c06f3fedab7c802927c2e00f941e740c1c 100644
--- a/src/Makefile.MESONH.mk
+++ b/src/Makefile.MESONH.mk
@@ -67,7 +67,7 @@ endif
 #
 DIR_SURFEX += ARCH_SRC/surfex
 DIR_SURFEX += SURFEX
-#CPPFLAGS_SURFEX=
+CPPFLAGS_SURFEX += -DMNH_PARALLEL
 #
 ifdef DIR_SURFEX
 DIR_MASTER += $(DIR_SURFEX)