diff --git a/pre-process.c b/pre-process.c
index fb3430a..73a58be 100644
--- a/pre-process.c
+++ b/pre-process.c
@@ -573,6 +573,9 @@ static struct token **substitute(struct token **list, struct token *body, struct
 		case TOKEN_MACRO_ARGUMENT:
 			arg = args[body->argnum].expanded;
 			count = &args[body->argnum].n_normal;
+			if (preprocess_hook) {
+				preprocess_hook->substitute_arg (&added, &args[body->argnum].expanded);
+			}
 			if (eof_token(arg)) {
 				state = Normal;
 				continue;
@@ -650,7 +653,7 @@ static int expand(struct token **list, struct symbol *sym)
 		if (preprocess_hook && preprocess_hook->expand_arg) {
 			int i;
 			for (i = 0; i < nargs; i++) {
-				preprocess_hook->expand_arg(token, sym, i, args[i].orig, args[i].expanded);
+				preprocess_hook->expand_arg(token, sym, i, args[i].orig, &args[i].expanded);
 				free_preprocessor_line(args[i].orig);
 			}
 		}
diff --git a/token.h b/token.h
index 985d1f5..c45d6be 100644
--- a/token.h
+++ b/token.h
@@ -175,7 +175,8 @@ struct preprocess_hook {
 	void (*expand_macro)(struct token *macro, struct symbol *sym, struct token *parent,
 			     struct token **replace, struct token **replace_tail);
 	void (*expand_arg)(struct token *macro, struct symbol *sym, int arg,
-			   struct token *orig, struct token *expanded);
+			   struct token *orig, struct token **expanded);
+	void (*substitute_arg)(struct token **dest, struct token **argp);
 };
 
 #define MAX_STRING 4095