diff --git a/Formula/d/darcs.rb b/Formula/d/darcs.rb
index ac4e7edd0606..359da8a2b289 100644
--- a/Formula/d/darcs.rb
+++ b/Formula/d/darcs.rb
@@ -15,12 +15,23 @@ class Darcs < Formula
   end
 
   depends_on "cabal-install" => :build
-  depends_on "ghc@9.8" => :build
+  depends_on "ghc@9.10" => :build
   depends_on "gmp"
 
   uses_from_macos "ncurses"
   uses_from_macos "zlib"
 
+  # Backport fixes for newer GHC[^1] and Cabal[^2]. Darcs uses a different
+  # patch file format and cannot be applied with the external patch DSL.
+  #
+  # * darcs diff --hash 32646b190e019de21a103e950c4eccdd66f7eadc
+  # * darcs diff --hash 50d9b0b402a896c83aa7929a50a0e0449838600f
+  # * darcs diff --hash 8da98f5de14034aa79a2860212fa34e99585e188
+  #
+  # [^1]: https://bugs.darcs.net/patch2422
+  # [^2]: https://bugs.darcs.net/patch2426
+  patch :DATA
+
   def install
     system "cabal", "v2-update"
     system "cabal", "v2-install", *std_cabal_v2_args
@@ -29,13 +40,85 @@ def install
   test do
     mkdir "my_repo" do
       system bin/"darcs", "init"
-      (Pathname.pwd/"foo").write "hello homebrew!"
+      Pathname("foo").write "hello homebrew!"
       system bin/"darcs", "add", "foo"
       system bin/"darcs", "record", "-am", "add foo", "--author=homebrew"
     end
     system bin/"darcs", "get", "my_repo", "my_repo_clone"
-    cd "my_repo_clone" do
-      assert_match "hello homebrew!", (Pathname.pwd/"foo").read
-    end
+    assert_equal "hello homebrew!", (testpath/"my_repo_clone/foo").read
   end
 end
+
+__END__
+diff -rN -u old-darcs.net/darcs.cabal new-darcs.net/darcs.cabal
+--- old-darcs.net/darcs.cabal	2025-01-05 10:09:26
++++ new-darcs.net/darcs.cabal	2025-01-05 10:09:26
+@@ -123,7 +123,7 @@
+ -- ----------------------------------------------------------------------
+ 
+ custom-setup
+-    setup-depends: base      >= 4.10 && < 4.20,
++    setup-depends: base      >= 4.10 && < 4.21,
+                    Cabal     >= 2.4 && < 3.11,
+                    process   >= 1.2.3.0 && < 1.7,
+                    filepath  >= 1.4.1 && < 1.5.0.0,
+@@ -412,7 +412,7 @@
+     else
+       build-depends:  unix >= 2.7.1.0 && < 2.9
+ 
+-    build-depends:    base              >= 4.10 && < 4.20,
++    build-depends:    base              >= 4.10 && < 4.21,
+                       safe              >= 0.3.20 && < 0.4,
+                       stm               >= 2.1 && < 2.6,
+                       binary            >= 0.5 && < 0.11,
+diff -rN -u old-darcs.net/Setup.hs new-darcs.net/Setup.hs
+--- old-darcs.net/Setup.hs	2025-01-05 10:24:34
++++ new-darcs.net/Setup.hs	2025-01-05 10:24:34
+@@ -8,7 +8,7 @@
+ import Distribution.Package ( packageVersion )
+ import Distribution.Version( Version )
+ import Distribution.Simple.LocalBuildInfo
+-         ( LocalBuildInfo(..), absoluteInstallDirs )
++         ( LocalBuildInfo(..), absoluteInstallDirs, buildDir )
+ import Distribution.Simple.InstallDirs (mandir, CopyDest (NoCopyDest))
+ import Distribution.Simple.Setup
+     (buildVerbosity, copyDest, copyVerbosity, fromFlag,
+diff -rN -u old-darcs.net/darcs.cabal new-darcs.net/darcs.cabal
+--- old-darcs.net/darcs.cabal	2025-01-05 10:24:34
++++ new-darcs.net/darcs.cabal	2025-01-05 10:24:34
+@@ -124,7 +124,7 @@
+ 
+ custom-setup
+     setup-depends: base      >= 4.10 && < 4.21,
+-                   Cabal     >= 2.4 && < 3.11,
++                   Cabal     >= 2.4 && < 3.13,
+                    process   >= 1.2.3.0 && < 1.7,
+                    filepath  >= 1.4.1 && < 1.5.0.0,
+                    directory >= 1.2.7 && < 1.4
+diff -rN -u old-darcs.net/darcs.cabal new-darcs.net/darcs.cabal
+--- old-darcs.net/darcs.cabal	2025-01-05 10:13:57
++++ new-darcs.net/darcs.cabal	2025-01-05 10:13:57
+@@ -464,9 +464,9 @@
+     if impl(ghc >= 9.8)
+       cpp-options:    -DHAVE_CRYPTON_CONNECTION
+       build-depends:  crypton-connection >= 0.4 && < 0.5,
+-                      data-default-class >= 0.1.2.0 && < 0.1.3,
++                      data-default      >= 0.7.1.3 && < 0.9,
+                       http-client-tls   >= 0.3.5 && < 0.4,
+-                      tls               >= 2.0.6 && < 2.1
++                      tls               >= 2.0.6 && < 2.2
+     else
+       -- cannot use crypton-connection >= 0.4, so
+       -- constraining indirect dependency to work around problems
+diff -rN -u old-darcs.net/src/Darcs/Util/HTTP.hs new-darcs.net/src/Darcs/Util/HTTP.hs
+--- old-darcs.net/src/Darcs/Util/HTTP.hs	2025-01-05 10:13:57
++++ new-darcs.net/src/Darcs/Util/HTTP.hs	2025-01-05 10:13:57
+@@ -46,7 +46,7 @@
+     )
+ 
+ #ifdef HAVE_CRYPTON_CONNECTION
+-import Data.Default.Class ( def )
++import Data.Default ( def )
+ import qualified Network.Connection as NC
+ import Network.HTTP.Client.TLS
+     ( mkManagerSettings