diff --git a/ompi/datatype/dt_arch.h b/ompi/datatype/dt_arch.h
index 559d98675b..2bd497317f 100644
--- a/ompi/datatype/dt_arch.h
+++ b/ompi/datatype/dt_arch.h
@@ -195,7 +195,7 @@
 
 #define OMPI_ARCH_ISBIGENDIAN     0x00000008
 #define OMPI_ARCH_LONGIS64        0x00000200
-#define OMPI_ARCH_LONGLONGISxx    0x0
+#define OMPI_ARCH_LONGLONGISxx    0x0000F000  /* the size of the long long */
 #define OMPI_ARCH_LONGDOUBLEIS96  0x00020000
 #define OMPI_ARCH_LONGDOUBLEIS128 0x00010000