diff --git a/PDP11/pdp11_dmc.c b/PDP11/pdp11_dmc.c
index 62639a65..a7785579 100644
--- a/PDP11/pdp11_dmc.c
+++ b/PDP11/pdp11_dmc.c
@@ -3823,7 +3823,7 @@ sprintf (attach_string, "Line=%d,Connect=%s,%s", dmc, peer, cptr);
 ans = tmxr_open_master (mp, attach_string);                 /* open master socket */
 if (ans != SCPE_OK)
     return ans;
-strncpy (port, cptr, CBUFSIZE-1);
+strncpy (port, cptr, sizeof(dmc_port[0]));
 uptr->filename = (char *)malloc (strlen(port)+1);
 strcpy (uptr->filename, port);
 uptr->flags |= UNIT_ATT;