diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,14 @@
 and this project adheres to the
 [Haskell Package Versioning Policy](https://pvp.haskell.org/).
 
+Any change that effects the number of holidays in a federal state must
+be reflected a minor version increment.
+
+## [2.1.0.0] - 2025-04-18
+
+Increment minor version because version 2.0.1.0 changed the number of
+holidays in Sachsen.
+
 ## [2.0.1.0] - 2025-04-17
 
 ### Fixed
diff --git a/bank-holiday-germany.cabal b/bank-holiday-germany.cabal
--- a/bank-holiday-germany.cabal
+++ b/bank-holiday-germany.cabal
@@ -1,7 +1,7 @@
 cabal-version:       3.6
 
 name:                bank-holiday-germany
-version:             2.0.1.0
+version:             2.1.0.0
 synopsis:            German bank holidays and public holidays
 description:         Calculation of bank holidays and public holidays in Germany.
 homepage:            https://github.com/schoettl/bank-holiday-germany#readme
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -23,6 +23,9 @@
 year :: Day -> Year
 year = (\(y, _, _) -> y) . toGregorian
 
+isSubsetOf :: Eq a => [a] -> [a] -> Bool
+isSubsetOf xs ys = all (\x -> x `elem` ys) xs
+
 holidaysBetween' :: FederalState -> Day -> Day -> [(Day, Holiday)]
 holidaysBetween' state x y = filter (isFederalPublicHoliday state . snd) $ holidaysBetween x y
 
@@ -75,6 +78,12 @@
       it "the only bank holidays that are no public holidays are Chrismas Eve and New Year's Eve" $
         length (filter (\x -> isBankHoliday x && not (isGermanPublicHoliday x)) [minBound..maxBound])
           `shouldBe` 2
+      it "holidays where isGermanPublicHoliday is true are public holidays in all federal states" $ hedgehog $ do
+        y <- forAll $ Gen.integral (Range.linear 0 5000)
+        let allHolidays = map snd $ holidaysBetween (fromGregorian y 1 1) (fromGregorian y 12 31)
+        let allStates = [minBound..maxBound] :: [FederalState]
+        all (\bundesland -> filter isGermanPublicHoliday allHolidays `isSubsetOf` filter (isFederalPublicHoliday bundesland) allHolidays) allStates
+           === True
     describe "yearFromDay" $ do
       it "works for any year" $ hedgehog $ do
         y <- forAll $ Gen.integral (Range.linear 0 5000)
@@ -155,3 +164,8 @@
     describe "germanHolidayName" $
       it "names are longer than 5 characters for all holidays (which mean there are no non-exhaustive patterns)" $
         all ((>5) . length . germanHolidayName) [minBound .. maxBound :: Holiday] `shouldBe` True
+    describe "isSubsetOf" $ do
+      it "is True for simple case" $
+        [1::Int] `isSubsetOf` [1,2] `shouldBe` True
+      it "is False for simple case" $
+        [3::Int] `isSubsetOf` [1,2] `shouldBe` False