diff --git a/base.cabal b/base.cabal
--- a/base.cabal
+++ b/base.cabal
@@ -4,7 +4,7 @@
 -- Make sure you are editing ghc-experimental.cabal.in, not ghc-experimental.cabal
 
 name:           base
-version:        4.21.0.0
+version:        4.21.1.0
 -- NOTE: Don't forget to update ./changelog.md
 
 license:        BSD-3-Clause
@@ -30,7 +30,7 @@
     default-language: Haskell2010
     default-extensions: NoImplicitPrelude
     build-depends:
-        ghc-internal == 9.1201.*,
+        ghc-internal == 9.1203.*,
         ghc-prim,
 
     exposed-modules:
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,7 +1,12 @@
 # Changelog for [`base` package](http://hackage.haskell.org/package/base)
 
-## 4.21.0.0 December 2024
+## 4.21.1.0 *Sept 2024*
+  * Fix incorrect results of `integerPowMod` when the base is 0 and the exponent is negative, and `integerRecipMod` when the modulus is zero ([#26017](https://gitlab.haskell.org/ghc/ghc/-/issues/26017)).
+  * Fix bug where `naturalAndNot` was incorrectly truncating results ([CLC proposal #350](github.com/haskell/core-libraries-committee/issues/350))
+
+## 4.21.0.0 *December 2024*
   * Shipped with GHC 9.12.1
+  * Change `SrcLoc` to be a strict and unboxed (finishing [CLC proposal #55](https://github.com/haskell/core-libraries-committee/issues/55))
   * Introduce `Data.Bounded` module exporting the `Bounded` typeclass (finishing [CLC proposal #208](https://github.com/haskell/core-libraries-committee/issues/208))
   * Deprecate export of `Bounded` class from `Data.Enum` ([CLC proposal #208](https://github.com/haskell/core-libraries-committee/issues/208))
   * `GHC.Desugar` has been deprecated and should be removed in GHC 9.14. ([CLC proposal #216](https://github.com/haskell/core-libraries-committee/issues/216))
@@ -409,6 +414,13 @@
       and ```\x y -> complement (x `xor` y)```, respectively.
 
     - `oneBits :: FiniteBits a => a`, `oneBits = complement zeroBits`.
+
+  * Various folding operations in `GHC.List` are now implemented via strict
+    folds:
+    - `sum`
+    - `product`
+    - `maximum`
+    - `minimum`
 
 ## 4.15.0.0 *Feb 2021*
 
diff --git a/src/GHC/Base.hs b/src/GHC/Base.hs
--- a/src/GHC/Base.hs
+++ b/src/GHC/Base.hs
@@ -278,7 +278,7 @@
 import GHC.Internal.Maybe
 import GHC.Types hiding (
   Unit#,
-  Solo#,
+  Solo#(..),
   Tuple0#,
   Tuple1#,
   Tuple2#,
diff --git a/src/GHC/Exts.hs b/src/GHC/Exts.hs
--- a/src/GHC/Exts.hs
+++ b/src/GHC/Exts.hs
@@ -267,7 +267,7 @@
   -- GHC's internal representation of 'TyCon's, for 'Typeable'
   Module, TrName, TyCon, TypeLitSort, KindRep, KindBndr,
   Unit#,
-  Solo#,
+  Solo#(..),
   Tuple0#,
   Tuple1#,
   Tuple2#,