diff --git a/src/currency.cpp b/src/currency.cpp
index bae5f08d12..e812538e3e 100644
--- a/src/currency.cpp
+++ b/src/currency.cpp
@@ -10,6 +10,8 @@
 /** @file currency.cpp Support for different currencies. */
 
 #include "stdafx.h"
+#include "core/bitmath_func.hpp"
+
 #include "currency.h"
 #include "news_func.h"
 #include "settings_type.h"
@@ -107,9 +109,9 @@ byte GetNewgrfCurrencyIdConverted(byte grfcurr_id)
  * get a mask of the allowed currencies depending on the year
  * @return mask of currencies
  */
-uint GetMaskOfAllowedCurrencies()
+uint64 GetMaskOfAllowedCurrencies()
 {
-	uint mask = 0;
+	uint64 mask = 0LL;
 	uint i;
 
 	for (i = 0; i < CURRENCY_END; i++) {
@@ -117,9 +119,9 @@ uint GetMaskOfAllowedCurrencies()
 
 		if (to_euro != CF_NOEURO && to_euro != CF_ISEURO && _cur_year >= to_euro) continue;
 		if (to_euro == CF_ISEURO && _cur_year < 2000) continue;
-		mask |= (1 << i);
+		SetBit(mask, i);
 	}
-	mask |= (1 << CURRENCY_CUSTOM); // always allow custom currency
+	SetBit(mask, CURRENCY_CUSTOM); // always allow custom currency
 	return mask;
 }
 
diff --git a/src/currency.h b/src/currency.h
index c4476b767b..aa29efdf7f 100644
--- a/src/currency.h
+++ b/src/currency.h
@@ -85,7 +85,7 @@ extern CurrencySpec _currency_specs[CURRENCY_END];
 #define _custom_currency (_currency_specs[CURRENCY_CUSTOM])
 #define _currency ((const CurrencySpec*)&_currency_specs[GetGameSettings().locale.currency])
 
-uint GetMaskOfAllowedCurrencies();
+uint64 GetMaskOfAllowedCurrencies();
 void CheckSwitchToEuro();
 void ResetCurrencies(bool preserve_custom = true);
 StringID *BuildCurrencyDropdown();
diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
index 50b0b880c0..3a20f455f6 100644
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -189,7 +189,7 @@ struct GameOptionsWindow : Window {
 				list = new DropDownList();
 				*selected_index = this->opt->locale.currency;
 				StringID *items = BuildCurrencyDropdown();
-				uint disabled = _game_mode == GM_MENU ? 0 : ~GetMaskOfAllowedCurrencies();
+				uint64 disabled = _game_mode == GM_MENU ? 0LL : ~GetMaskOfAllowedCurrencies();
 
 				/* Add non-custom currencies; sorted naturally */
 				for (uint i = 0; i < CURRENCY_END; items++, i++) {