diff -r 9f73edc0c57a -r c9fdeb7450da src/ai/api/ai_town.cpp
--- a/src/ai/api/ai_town.cpp	Tue Apr 15 22:18:11 2008 +0000
+++ b/src/ai/api/ai_town.cpp	Tue Apr 15 22:29:00 2008 +0000
@@ -39,7 +39,7 @@
 
 /* static */ int32 AITown::GetPopulation(TownID town_id)
 {
-	if (!IsValidTown(town_id)) return 0;
+	if (!IsValidTown(town_id)) return -1;
 	const Town *t = ::GetTown(town_id);
 	return t->population;
 }