diff --git a/admin/Makefile.def b/admin/Makefile.def
index 0395d9d4f0..932d18f102 100644
--- a/admin/Makefile.def
+++ b/admin/Makefile.def
@@ -228,7 +228,11 @@ GLOBAL_DIRTY = $(builddir) *~ TAGS ChangeLog* Makefile.bak
 # Fortran preprocessing
 
 # Preprocessor command
-CPP = cpp
+ifdef GAG_CPP
+   CPP = $(GAG_CPP)
+else
+   CPP = cpp
+endif
 
 # Preprocessor generic flags
 GLOBAL_CPPFLAGS += -P -traditional -C