diff --git a/Documentation/serial/tty.txt b/Documentation/serial/tty.txt
index 7c90050..540db41 100644
--- a/Documentation/serial/tty.txt
+++ b/Documentation/serial/tty.txt
@@ -107,7 +107,7 @@
 
 dcd_change()	-	Report to the tty line the current DCD pin status
 			changes and the relative timestamp. The timestamp
-			can be NULL.
+			cannot be NULL.
 
 
 Driver Access