diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index b6fcf58c7d..75adad35f4 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2019-06-18  Tom Tromey  <tromey@adacore.com>
+
+	* gdb.base/list0.h: Add comment explaining control character.
+
 2019-06-18  Tom de Vries  <tdevries@suse.de>
 
 	* boards/fission.exp: Break up long debug_flags line.
diff --git a/gdb/testsuite/gdb.base/list0.h b/gdb/testsuite/gdb.base/list0.h
index 6f28093550..ba18e29268 100644
--- a/gdb/testsuite/gdb.base/list0.h
+++ b/gdb/testsuite/gdb.base/list0.h
@@ -2,7 +2,7 @@
 
 extern void bar(int);
 static void foo (int x)
-/* !
+/* ! the next line has a control character, see PR symtab/24423.
 
    ! */
 {