diff --git a/mkpasswd.1 b/mkpasswd.1
index db7db47..86a949c 100644
--- a/mkpasswd.1
+++ b/mkpasswd.1
@@ -20,6 +20,7 @@ Use the \fISTRING\fP as salt. It must not contain prefixes such as \fI$1$\fP.
 Use \fINUMBER\fP rounds. This argument is ignored if the method chosen
 does not support variable rounds. For the OpenBSD Blowfish method this is
 the logarithm of the number of rounds.
+The behavior is undefined if this option is used without \fI--method\fP.
 .TP
 .B -m, --method=TYPE
 Compute the password using the \fITYPE\fP method.