diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+# v1.1.2.4
+
+- Adds support for `ghc` 9.12 and `base` 4.21.
+
 # v1.1.2.3
 
 - Adds support for `ghc` 9.8 and 9.10, `base` 4.19 and 4.20, and `containers` 0.7.
diff --git a/fused-effects.cabal b/fused-effects.cabal
--- a/fused-effects.cabal
+++ b/fused-effects.cabal
@@ -1,7 +1,7 @@
 cabal-version:       2.2
 
 name:                fused-effects
-version:             1.1.2.3
+version:             1.1.2.4
 synopsis:            A fast, flexible, fused effect system.
 description:         A fast, flexible, fused effect system, à la Effect Handlers in Scope, Monad Transformers and Modular Algebraic Effects: What Binds Them Together, and Fusion for Free—Efficient Algebraic Effect Handlers.
 homepage:            https://github.com/fused-effects/fused-effects
@@ -9,7 +9,7 @@
 license-file:        LICENSE
 author:              Nicolas Wu, Tom Schrijvers, Rob Rix, Patrick Thomson
 maintainer:          robrix@github.com
-copyright:           2018-2023 Nicolas Wu, Tom Schrijvers, Rob Rix, Patrick Thomson
+copyright:           2018-2025 Nicolas Wu, Tom Schrijvers, Rob Rix, Patrick Thomson
 category:            Control
 build-type:          Simple
 extra-source-files:
@@ -29,6 +29,7 @@
   GHC == 9.6.2
   GHC == 9.8.2
   GHC == 9.10.1
+  GHC == 9.12.1
 
 common common
   default-language: Haskell2010
@@ -63,7 +64,7 @@
       -Wno-missing-role-annotations
       -Wno-term-variable-capture
       -Wno-x-partial
-      -Wno-missing-poly-kind-signatures  
+      -Wno-missing-poly-kind-signatures
 
 library
   import:         common
@@ -133,7 +134,7 @@
     Control.Effect.Throw.Internal
     Control.Effect.Writer.Internal
   build-depends:
-      base          >= 4.9 && < 4.21
+      base          >= 4.9 && < 4.22
     , transformers  >= 0.4 && < 0.7
     , unliftio-core >= 0.2 && < 0.3