diff --git a/PDP18B/pdp18b_dt.c b/PDP18B/pdp18b_dt.c
index 264cbf91..ae2c40e1 100644
--- a/PDP18B/pdp18b_dt.c
+++ b/PDP18B/pdp18b_dt.c
@@ -995,7 +995,8 @@ switch (fnc) {                                          /* at speed, check fnc *
                 fprintf (sim_deb, ">>DT%d: reading block %d %s%s\n",
                          unum, blk, (dir? "backward": "forward"),
                          ((dtsa & DTA_MODE)? " continuous": " "));
-            dt_substate = 0;                            /* fall through */
+            dt_substate = 0;
+            /* fall through */
         case 0:                                         /* normal read */
             M[DT_WC] = (M[DT_WC] + 1) & DMASK;          /* incr WC, CA */
             M[DT_CA] = (M[DT_CA] + 1) & DMASK;
@@ -1058,6 +1059,7 @@ switch (fnc) {                                          /* at speed, check fnc *
         case 0:                                         /* normal write */
             M[DT_WC] = (M[DT_WC] + 1) & DMASK;          /* incr WC, CA */
             M[DT_CA] = (M[DT_CA] + 1) & DMASK;
+            /* fall through */
         case DTO_WCO:                                   /* wc ovflo */
             ma = M[DT_CA] & AMASK;                      /* mem addr */
             ba = (blk * DTU_BSIZE (uptr)) + wrd;        /* buffer ptr */