diff --git a/ChangeLog b/ChangeLog
index ce0266a35e..a514dd69a6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2018-06-20  Joseph Myers  <joseph@codesourcery.com>
 
+	* string/tst-cmp.c: Include <libc-diag.h>.
+	(strncmp_max): Disable -Wstringop-overflow= around call to
+	strncmp.
+	(strncasecmp_max): Disable -Wstringop-overflow= around call to
+	strncasecmp.
+
 	* string/bug-strpbrk1.c: Include <libc-diag.h>.
 	(main): Disable -Wunused-value around call to strpbrk.
 	* string/bug-strspn1.c: Include <libc-diag.h>.
diff --git a/string/tst-cmp.c b/string/tst-cmp.c
index 1a7f1c8b89..3b9f7b2506 100644
--- a/string/tst-cmp.c
+++ b/string/tst-cmp.c
@@ -26,6 +26,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <libc-diag.h>
 
 static int
 signum (int val)
@@ -98,13 +99,27 @@ strncasecmp_64 (const char *left, const char *right)
 static int
 strncmp_max (const char *left, const char *right)
 {
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 9 warns about the size passed to strncmp being larger than
+     PTRDIFF_MAX; the use of SIZE_MAX is deliberate here.  */
+  DIAG_IGNORE_NEEDS_COMMENT (9, "-Wstringop-overflow=");
+#endif
   return strncmp (left, right, SIZE_MAX);
+  DIAG_POP_NEEDS_COMMENT;
 }
 
 static int
 strncasecmp_max (const char *left, const char *right)
 {
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 9 warns about the size passed to strncasecmp being larger
+     than PTRDIFF_MAX; the use of SIZE_MAX is deliberate here.  */
+  DIAG_IGNORE_NEEDS_COMMENT (9, "-Wstringop-overflow=");
+#endif
   return strncasecmp (left, right, SIZE_MAX);
+  DIAG_POP_NEEDS_COMMENT;
 }
 
 int