Darklands Puzzle #33

The path is blocked by a grim iron door. Carved overhead are the words:
EACH STATUE SPEAKS EITHER ALL TRUTH OR ALL LIES.
PUSH A STATUE TO PASS.
Standing by on the door are two statues: one of a dwarf, the other of a kobold.
The dwarf statue says, "The statue which opens the door always lies."
Which statue should you push? A mistake could (will. ed.) release a trap! You think carefully, then press...
...the dwarf statue.
...the kobold statue.

(Source: Darklands cluebook by MicroProse Software)

If the dwarf is lying then one must press the kobold statue, as the dwarf statue would be telling the truth if pressing it opened the door. If, on the other hand, the dwarf is telling the truth then one must still press the kobold statue, as the dwarf statue would be implicating itself as a liar if pressing it opened the door, which is not possible.