diff --git a/src/command_type.h b/src/command_type.h
index 240c9f615c..19132a27f2 100644
--- a/src/command_type.h
+++ b/src/command_type.h
@@ -35,13 +35,13 @@ public:
 	/**
 	 * Creates a command return value the is failed with the given message
 	 */
-	CommandCost(StringID msg) : expense_type(INVALID_EXPENSES), cost(0), message(msg), success(false) {}
+	explicit CommandCost(StringID msg) : expense_type(INVALID_EXPENSES), cost(0), message(msg), success(false) {}
 
 	/**
 	 * Creates a command cost with given expense type and start cost of 0
 	 * @param ex_t the expense type
 	 */
-	CommandCost(ExpensesType ex_t) : expense_type(ex_t), cost(0), message(INVALID_STRING_ID), success(true) {}
+	explicit CommandCost(ExpensesType ex_t) : expense_type(ex_t), cost(0), message(INVALID_STRING_ID), success(true) {}
 
 	/**
 	 * Creates a command return value with the given start cost and expense type