diff --git a/src/mkroom.c b/src/mkroom.c
index 229ff97a2..53828b12e 100644
--- a/src/mkroom.c
+++ b/src/mkroom.c
@@ -543,6 +543,7 @@ mkswamp(void) /* Michiel Huisjes & Fred de Wilde */
                 if (!OBJ_AT(sx, sy) && !MON_AT(sx, sy) && !t_at(sx, sy)
                     && !nexttodoor(sx, sy)) {
                     if ((sx + sy) % 2) {
+                        del_engr_at(sx, sy);
                         levl[sx][sy].typ = POOL;
                         if (!eelct || !rn2(4)) {
                             /* mkclass() won't do, as we might get kraken */