diff -ru exim-4.92.orig/src/exim.c exim-4.92/src/exim.c
--- exim-4.92.orig/src/exim.c	2019-02-11 13:17:06.489418000 +0100
+++ exim-4.92/src/exim.c	2019-02-11 13:34:50.663777000 +0100
@@ -683,6 +683,9 @@
 
 
 /* Print error string, then die */
+#ifdef __GNUC__
+static void exim_fail(const char * fmt, ...) __attribute__((format (printf, 1, 2)));
+#endif
 static void
 exim_fail(const char * fmt, ...)
 {