https://svnweb.freebsd.org/ports/head/games/frobtads/files/patch-tads3_vmtz.cpp?revision=432973&view=markup

diff -u -r ../frobtads-1.2.3/tads3/vmtz.cpp ./tads3/vmtz.cpp
--- ../frobtads-1.2.3/tads3/vmtz.cpp	2013-05-17 21:46:51.000000000 +0200
+++ ./tads3/vmtz.cpp	2017-06-12 00:31:09.635744304 +0200
@@ -1984,7 +1984,7 @@
              *   the transition in terms of the local time that was in effect
              *   up until that moment
              */
-            result->set(tcur > 0 ? tcur - 1 : tcur);
+            result->set(cur > 0 ? tcur - 1 : tcur);
             return;
         }
     }