diff --git a/CHANGES b/CHANGES
--- a/CHANGES
+++ b/CHANGES
@@ -1,9 +1,16 @@
+* 0.6.4: 10 February 2025
+
+- New instance `Action m a => Action [m] a` (thanks to Manuel Bärenz for the suggestion)
+
 * 0.6.3: 8 August 2024
 
 - New instances (thanks to Clinton Mead):
   - `Action (First a) a`
   - `Action Void a`
   - `Action m a => Action (Identity m) a`
+
+- r1 (27 Jan 2025):
+  - Allow `base-4.21` and test on GHC 9.12.
 
 * 0.6.2: 20 Dec 2022
 
diff --git a/monoid-extras.cabal b/monoid-extras.cabal
--- a/monoid-extras.cabal
+++ b/monoid-extras.cabal
@@ -1,5 +1,5 @@
 name:                monoid-extras
-version:             0.6.3
+version:             0.6.4
 synopsis:            Various extra monoid-related definitions and utilities
 description:         Various extra monoid-related definitions and utilities,
                      such as monoid actions, monoid coproducts, semi-direct
@@ -14,7 +14,7 @@
 category:            Data
 build-type:          Simple
 cabal-version:       >=1.10
-tested-with:         GHC ==8.4.4 || ==8.6.5 || ==8.8.4 || ==8.10.7 || ==9.0.2 || ==9.2.8 || ==9.4.8 || ==9.6.5 || ==9.8.2 || ==9.10.1
+tested-with:         GHC ==8.4.4 || ==8.6.5 || ==8.8.4 || ==8.10.7 || ==9.0.2 || ==9.2.8 || ==9.4.8 || ==9.6.6 || ==9.8.2 || ==9.10.1 || ==9.12.1
 
 source-repository head
   type: git
@@ -36,7 +36,7 @@
                      Data.Monoid.Split,
                      Data.Monoid.WithSemigroup
 
-  build-depends:     base >= 4.11 && < 4.21,
+  build-depends:     base >= 4.11 && < 4.22,
                      groups < 0.6,
                      semigroupoids >= 4.0 && < 6.1
 
@@ -55,7 +55,7 @@
   hs-source-dirs: benchmarks
   main-is: SemiDirectProduct.hs
   type: exitcode-stdio-1.0
-  build-depends: base          >= 4.3 &&  < 4.21
+  build-depends: base          >= 4.3 &&  < 4.22
                , semigroups
                , criterion
                , monoid-extras
diff --git a/src/Data/Monoid/Action.hs b/src/Data/Monoid/Action.hs
--- a/src/Data/Monoid/Action.hs
+++ b/src/Data/Monoid/Action.hs
@@ -76,6 +76,10 @@
   act Nothing  s = s
   act (Just m) s = act m s
 
+-- | @act [a,b,c,...] = act a . act b . act c . ...@
+instance Action m s => Action [m] s where
+  act = flip (foldr act)
+
 -- | @Endo@ acts by application.
 --
 --   Note that in order for this instance to satisfy the @Action@