--- a/fortran/nf_logging.F90
+++ b/fortran/nf_logging.F90
@@ -1,3 +1,10 @@
+! This file is compiled only if logging is enabled. However, the macro LOGGING
+! is never defined. For most of the compilers this simply leads to an empty
+! object: they do not complain when a source file is empty. This is not the
+! case for NAG: the compiler fails the compilation of empty sources. To fix
+! this problem, we define the macro here.
+#define LOGGING
+
 #ifdef LOGGING
 ! Function to turn on logging
 !-------------------------------- nf_set_log_level ----------------------------