diff --git a/ChangeLog b/ChangeLog
index bc5ff14081..579185d23e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2017-11-14  Joseph Myers  <joseph@codesourcery.com>
+
+	* string/bug-strncat1.c: Include <libc-diag.h>.
+	(main): Disable -Wstringop-truncation for strncat call for GCC 8.
+
 2017-11-13  Claude Paroz <claude@2xlibre.net>
 
 	[BZ #22387]
diff --git a/string/bug-strncat1.c b/string/bug-strncat1.c
index f1b5c37c5c..b22beba4d3 100644
--- a/string/bug-strncat1.c
+++ b/string/bug-strncat1.c
@@ -4,13 +4,21 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <libc-diag.h>
 
 char d[3] = "\0\1\2";
 
 int
 main (void)
 {
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (8, 0)
+  /* GCC 8 warns about strncat truncating output; this is deliberately
+     tested here.  */
+  DIAG_IGNORE_NEEDS_COMMENT (8, "-Wstringop-truncation");
+#endif
   strncat (d, "\5\6", 1);
+  DIAG_POP_NEEDS_COMMENT;
   if (d[0] != '\5')
     {
       puts ("d[0] != '\\5'");