Index: frobtads/files/patch-tads3_vmtz.cpp
===================================================================
--- frobtads/files/patch-tads3_vmtz.cpp	(nonexistent)
+++ frobtads/files/patch-tads3_vmtz.cpp	(working copy)
@@ -0,0 +1,11 @@
+--- tads3/vmtz.cpp.orig	2017-02-01 00:03:18.317956000 +0100
++++ tads3/vmtz.cpp	2017-02-01 00:03:27.009520000 +0100
+@@ -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;
+         }
+     }