diff -Nurd -x'*~' grep-3.1.orig/gnulib-tests/vasnprintf.c grep-3.1/gnulib-tests/vasnprintf.c
--- grep-3.1.orig/gnulib-tests/vasnprintf.c	2017-05-20 20:32:47.000000000 -0400
+++ grep-3.1/gnulib-tests/vasnprintf.c	2017-12-30 17:56:06.000000000 -0500
@@ -4869,7 +4869,7 @@
 #endif
                   *fbp = dp->conversion;
 #if USE_SNPRINTF
-# if !(((__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3)) && !defined __UCLIBC__) || ((defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__))
+# if !defined(__APPLE__) && !(((__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3)) && !defined __UCLIBC__) || ((defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__))
                 fbp[1] = '%';
                 fbp[2] = 'n';
                 fbp[3] = '\0';