// [enne] - It's possible that mgrd and monster->x/y are out of
            // sync because they are updated separately.  If we can see this
            // monster, then make sure that the mgrd is set correctly.
            if (mgrd[monster->x][monster->y] != s)
            {
#ifdef DEBUG_DIAGNOSTICS
                // If this mprf triggers for you, please note any special
                // circumstances so we can track down where this is coming
                // from.
                mprf(MSGCH_DIAGNOSTICS, "monster (%d) at (%d, %d) was "
                     "improperly placed.  Updating mgrd.", s, 
                     monster->x, monster->y);
#endif
                ASSERT(mgrd[monster->x][monster->y] == NON_MONSTER);
                mgrd[monster->x][monster->y] = s;
            }