diff --git a/mediator/Makefile b/mediator/Makefile
index fae000dae..d40272a19 100644
--- a/mediator/Makefile
+++ b/mediator/Makefile
@@ -3,13 +3,14 @@ $(error Environment variable ESMFMKFILE was not set.)
 endif
 
 include $(ESMFMKFILE)
+CPPDEFS += -DESMF_VERSION_MAJOR=$(ESMF_VERSION_MAJOR) -DESMF_VERSION_MINOR=$(ESMF_VERSION_MINOR)
 
 ifndef PIO_INCLUDE_DIR
 $(error PIO_INCLUDE_DIR not set)
 endif
 
 ifdef INTERNAL_PIO_INIT
-CPPDEFS := -DINTERNAL_PIO_INIT
+CPPDEFS += -DINTERNAL_PIO_INIT
 endif
 
 LIBRARY := libcmeps.a