diff --git a/include/assert_macros.h b/include/assert_macros.h
index 4a058a9..63e014b 100644
--- a/include/assert_macros.h
+++ b/include/assert_macros.h
@@ -14,7 +14,7 @@
 ! Deal with stringification issues:
 ! https://gcc.gnu.org/legacy-ml/fortran/2009-06/msg00131.html
 #ifndef STRINGIFY
-# if defined(__GFORTRAN__) || defined(_CRAYFTN)
+# if defined(__GFORTRAN__) || defined(_CRAYFTN) || defined(NAGFOR)
 #  define STRINGIFY(x) "x"
 # else
 #  define STRINGIFY(x) #x