diff --git a/src/Rules.LXifort.mk b/src/Rules.LXifort.mk
index 665a1310746302d21689cf1337a96f87f50f2487..18e420ccca2d4ba3e37a0d8d00d888696f6cca48 100644
--- a/src/Rules.LXifort.mk
+++ b/src/Rules.LXifort.mk
@@ -77,6 +77,9 @@ endif
 else
 ifeq "$(VER_MPI)" "MPIINTEL"
 F90 = mpiifort
+ifeq "$(MNH_INT)" "I8"
+OPT_BASE         += -ilp64
+endif
 else
 F90 = ifort
 endif