diff --git a/src/ai/ai.cpp b/src/ai/ai.cpp
--- a/src/ai/ai.cpp
+++ b/src/ai/ai.cpp
@@ -81,10 +81,10 @@ static void AI_PutCommandInQueue(PlayerI
 /**
  * Executes a raw DoCommand for the AI.
  */
-int32 AI_DoCommandCc(TileIndex tile, uint32 p1, uint32 p2, uint32 flags, uint procc, CommandCallback* callback)
+CommandCost AI_DoCommandCc(TileIndex tile, uint32 p1, uint32 p2, uint32 flags, uint procc, CommandCallback* callback)
 {
 	PlayerID old_lp;
-	int32 res = 0;
+	CommandCost res = 0;
 	const char* tmp_cmdtext;
 
 	/* If you enable DC_EXEC with DC_QUERY_COST you are a really strange
@@ -135,7 +135,7 @@ int32 AI_DoCommandCc(TileIndex tile, uin
 }
 
 
-int32 AI_DoCommand(TileIndex tile, uint32 p1, uint32 p2, uint32 flags, uint procc)
+CommandCost AI_DoCommand(TileIndex tile, uint32 p1, uint32 p2, uint32 flags, uint procc)
 {
 	return AI_DoCommandCc(tile, p1, p2, flags, procc, NULL);
 }