diff --git a/API.md b/API.md
index 1a9426d..439b7fd 100644
--- a/API.md
+++ b/API.md
@@ -20,23 +20,38 @@ The calendar mod uses cardinal numbers internally to store the date internally,
 this is only done to make calculations a bit simpler.
 `total_days` is also a cardinal number.
 
-## Calendar configiguration
-In `gameconfig.lua`, there several variables that customize the calendar:
+## Calendar configuration
+Before calling any other function, you probably want to configure the calendar first.
+Call `calendar.config` to do so. This is not required, however, the calendar
+has a default configuration:
 
-* `calendar.MONTH_DAYS`: Days in a month
-* `calendar.month_names`: List of month names
-* `calendar.month_names_short`: List of short month names
-* `calendar.weekday_names`: List of weekday names
-* `calendar.weekday_names_short`: List of short weekday names
-* `calendar.FIRST_WEEK_DAY`: Cardinal number of the weekday that
-                             marks the beginning of a week
-                             and the calendar
-
-By default, a year has 12 months with 30 days each,
+By default, ayear has 12 months with 30 days each,
 the months are January to December,
 the week has 7 weekdays from Monday to Sunday, starting at Monday.
 
-For convenience, there are also these shortcuts, derived from the other values:
+### `calendar.config(config)`
+Configure calendar. Call this function before any other function.
+
+`config` is a table with the following fields (all fields are optional):
+
+* `MONTH_DAYS`: Days in a month
+* `month_names`: List of month names (also determines number of months)
+* `month_names_short`: List of short month names
+* `weekday_names`: List of weekday names (also determines number of weekdays)
+* `weekday_names_short`: List of short weekday names
+* `FIRST_WEEK_DAY`: Cardinal number of the weekday that
+                    marks the beginning of a week
+                    and the calendar
+
+Fields that were `nil` won't change. You can access each of the calender settings
+later with `calender.<field name>`, e.g. `calendar.MONTH_DAYS`. Note this is
+read-only access, you must never write to these fields directly. Only
+use `calendar.config` to change these fields.
+
+### Convenience variables
+For convenience, there are also these shortcuts that are automatically set,
+derived from the other values:
+
 * `calendar.MONTHS`: Number of months in a year
 * `calendar.WEEK_DAYS`: Number of days in a week
 * `calendar.YEAR_DAYS`: Number of days in a year
diff --git a/gameconfig.lua b/gameconfig.lua
index c4ad7af..4fa5564 100644
--- a/gameconfig.lua
+++ b/gameconfig.lua
@@ -1,9 +1,9 @@
 -- For translation collector script
 local N = function(s) return s end
 
-----------------------------------
--- BEGINNING OF CALENDAR CONFIG --
-----------------------------------
+-----------------------------
+-- DEFAULT CALENDAR CONFIG --
+-----------------------------
 
 -- Number of days in a month
 calendar.MONTH_DAYS = 30
diff --git a/init.lua b/init.lua
index 4bdd85b..697b615 100644
--- a/init.lua
+++ b/init.lua
@@ -34,15 +34,40 @@ local F = minetest.formspec_escape
 
 dofile(minetest.get_modpath("calendar").."/gameconfig.lua")
 
--- Number of months in a year
-calendar.MONTHS = #calendar.month_names
--- Number of days in a week
-calendar.WEEK_DAYS = #calendar.weekday_names
--- Number of days in a year
-calendar.YEAR_DAYS = calendar.MONTHS * calendar.MONTH_DAYS
+local function update_helper_vars()
+	-- Number of months in a year
+	calendar.MONTHS = #calendar.month_names
+	-- Number of days in a week
+	calendar.WEEK_DAYS = #calendar.weekday_names
+	-- Number of days in a year
+	calendar.YEAR_DAYS = calendar.MONTHS * calendar.MONTH_DAYS
+end
+update_helper_vars()
 
 local holidays = {}
 
+calendar.config = function(config)
+	if config.MONTH_DAYS then
+		calendar.MONTH_DAYS = config.MONTH_DAYS
+	end
+	if config.month_names then
+		calendar.month_names = config.month_names
+	end
+	if config.month_names_short then
+		calendar.month_names_short = config.month_names_short
+	end
+	if config.weekday_names then
+		calendar.weekday_names = config.weekday_names
+	end
+	if config.weekday_names_short then
+		calendar.weekday_names_short = config.weekday_names_short
+	end
+	if config.FIRST_WEEK_DAY then
+		calendar.FIRST_WEEK_DAY = config.FIRST_WEEK_DAY
+	end
+	update_helper_vars()
+end
+
 calendar.register_holiday = function(def)
 	table.insert(holidays, def)
 end