diff --git a/src/rrd_graph.c b/src/rrd_graph.c
index 2c4f71a..275a8c0 100644
--- a/src/rrd_graph.c
+++ b/src/rrd_graph.c
@@ -4191,7 +4191,7 @@ void rrd_graph_options(
         int       col_start, col_end;
 
         opt = getopt_long(argc, argv,
-                          "Aa:B:b:c:Dd:Ee:Ff:G:gh:IiJjL:l:Nn:Bb:oPR:rS:s:T:t:u:v:W:w:X:x:Yy:z",
+                          "Aa:B:b:c:Dd:Ee:Ff:G:gh:IiJjL:l:MNn:oPR:rS:s:T:t:u:v:W:w:X:x:Yy:z",
                           long_options, &option_index);
         if (opt == EOF)
             break;