Index: src/ai/ai_gui.cpp
===================================================================
--- src/ai/ai_gui.cpp	(revision 27529)
+++ src/ai/ai_gui.cpp	(working copy)
@@ -845,7 +845,7 @@
 				if (widget == WID_AIC_DECREASE) {
 					new_value = max(0, GetGameSettings().difficulty.max_no_competitors - 1);
 				} else {
-					new_value = min(MAX_COMPANIES - 1, GetGameSettings().difficulty.max_no_competitors + 1);
+					new_value = min(MAX_COMPANIES, GetGameSettings().difficulty.max_no_competitors + 1);
 				}
 				IConsoleSetSetting("difficulty.max_no_competitors", new_value);
 				this->InvalidateData();
@@ -922,7 +922,7 @@
 		if (!gui_scope) return;
 
 		this->SetWidgetDisabledState(WID_AIC_DECREASE, GetGameSettings().difficulty.max_no_competitors == 0);
-		this->SetWidgetDisabledState(WID_AIC_INCREASE, GetGameSettings().difficulty.max_no_competitors == MAX_COMPANIES - 1);
+		this->SetWidgetDisabledState(WID_AIC_INCREASE, GetGameSettings().difficulty.max_no_competitors == MAX_COMPANIES);
 		this->SetWidgetDisabledState(WID_AIC_CHANGE, (this->selected_slot == OWNER_DEITY && _game_mode == GM_NORMAL) || this->selected_slot == INVALID_COMPANY);
 		this->SetWidgetDisabledState(WID_AIC_CONFIGURE, this->selected_slot == INVALID_COMPANY || GetConfig(this->selected_slot)->GetConfigList()->size() == 0);
 		this->SetWidgetDisabledState(WID_AIC_MOVE_UP, this->selected_slot == OWNER_DEITY || this->selected_slot == INVALID_COMPANY || !IsEditable((CompanyID)(this->selected_slot - 1)));
Index: src/table/settings.ini
===================================================================
--- src/table/settings.ini	(revision 27529)
+++ src/table/settings.ini	(working copy)
@@ -103,7 +103,7 @@
 from     = 97
 def      = 0
 min      = 0
-max      = MAX_COMPANIES - 1
+max      = MAX_COMPANIES
 interval = 1
 proc     = MaxNoAIsChange
 cat      = SC_BASIC