Fix macro for checking strerror_r() variant

diff --git a/logging.c b/logging.c
index e2d190c..ede07e8 100644 (file)
--- a/logging.c
+++ b/logging.c
@@ -156,7 +156,7 @@ static void log_prefixed_system_error(FILE *file, int error_code, const char *pr
 
        char buf[1024] = {0};
        char *errno_msg;
-#if (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) && ! _GNU_SOURCE
+#if (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) && ! defined(_GNU_SOURCE)
        int ret = strerror_r(error_code, buf, sizeof(buf));
        errno_msg = ret == 0 ? buf : "<strerror_r failure>";
 #else