The Wizard and the War Machine — Lawrence Watt-Evans

Stranded for a decade on the planet Dest, Sam Turner, formerly Slant the cyborg and now a practicing wizard, never expected to see another Earth-human again. So when his internal communication circuit suddenly picked up a call from an independent Reconnaisance Unit cyborg like himself, he was perplexed--and concerned. For it fast became clear that the new arrival, Flame, was sure that any populated planet must be enemy to the long-vanquished Old Earth--and thus was bent on Dest's total destruction. Only Turner could stop Flame. But he was out-armed by her ship, and he could not use magic since Flame's computer would interpret that as an enemy attack.