diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index fd559a7..dcbfcf0 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -82,7 +82,8 @@
  *            the HkdfLabel structure on success.
  */
 
-static const char tls13_label_prefix[6] = "tls13 ";
+/* We need to tell the compiler that we meant to leave out the null character. */
+static const char tls13_label_prefix[6] __attribute__ ((nonstring)) = "tls13 ";
 
 #define SSL_TLS1_3_KEY_SCHEDULE_HKDF_LABEL_LEN(label_len, context_len) \
     (2                     /* expansion length           */ \