diff --git a/src/ai/ai_gui.cpp b/src/ai/ai_gui.cpp
--- a/src/ai/ai_gui.cpp
+++ b/src/ai/ai_gui.cpp
@@ -280,7 +280,7 @@ struct AIConfigWindow : public Window {
 		this->SetWidgetDisabledState(WID_AIC_DECREASE_INTERVAL, GetGameSettings().difficulty.competitors_interval == MIN_COMPETITORS_INTERVAL);
 		this->SetWidgetDisabledState(WID_AIC_INCREASE_INTERVAL, GetGameSettings().difficulty.competitors_interval == MAX_COMPETITORS_INTERVAL);
 		this->SetWidgetDisabledState(WID_AIC_CHANGE, this->selected_slot == INVALID_COMPANY);
-		this->SetWidgetDisabledState(WID_AIC_CONFIGURE, this->selected_slot == INVALID_COMPANY || AIConfig::GetConfig(this->selected_slot)->GetConfigList()->size() == 0);
+		this->SetWidgetDisabledState(WID_AIC_CONFIGURE, this->selected_slot == INVALID_COMPANY || AIConfig::GetConfig(this->selected_slot)->GetConfigList()->empty());
 		this->SetWidgetDisabledState(WID_AIC_MOVE_UP, this->selected_slot == INVALID_COMPANY || !IsEditable((CompanyID)(this->selected_slot - 1)));
 		this->SetWidgetDisabledState(WID_AIC_MOVE_DOWN, this->selected_slot == INVALID_COMPANY || !IsEditable((CompanyID)(this->selected_slot + 1)));