diff --git a/.github/workflows/riscv64-cross-ci.yml b/.github/workflows/riscv64-cross-ci.yml
new file mode 100644
index 0000000..928521c
--- /dev/null
+++ b/.github/workflows/riscv64-cross-ci.yml
@@ -0,0 +1,49 @@
+name: RISC-V 64bit cross-compiler CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Prepare git
+        run:
+          git config --global url."git://github.com/ghc/packages-".insteadOf     git://github.com/ghc/packages/ &&
+          git config --global url."http://github.com/ghc/packages-".insteadOf    http://github.com/ghc/packages/ &&
+          git config --global url."https://github.com/ghc/packages-".insteadOf   https://github.com/ghc/packages/ &&
+          git config --global url."ssh://git@github.com/ghc/packages-".insteadOf ssh://git@github.com/ghc/packages/ &&
+          git config --global url."git@github.com:ghc/packages-".insteadOf       git@github.com:ghc/packages/
+
+      - name: Checkout GHC
+        uses: actions/checkout@v2.4.0
+        with:
+          repository: ghc/ghc
+          submodules: recursive
+
+      - name: Checkout ghc.nix
+        uses: actions/checkout@v2.4.0
+        with:
+          path: ghc.nix
+
+      - name: Install nix
+        uses: cachix/install-nix-action@v20
+
+      - name: Use cachix
+        uses: cachix/cachix-action@v12
+        with:
+          name: ghc-nix
+          signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
+
+      - name: Run nix-shell - Boot and Configure
+        run: nix-shell --pure ghc.nix/shell.nix --arg withLlvm true --arg crossTarget '"riscv64"' --command "./boot && configure_ghc"
+
+      - name: Run nix-shell - cabal update
+        run: nix-shell --pure ghc.nix/shell.nix --arg withLlvm true --arg crossTarget '"riscv64"' --command "pushd hadrian; cabal update; popd"
+
+      - name: Run nix-shell - Build GHC
+        run: nix-shell --pure ghc.nix/shell.nix  --arg withLlvm true --arg crossTarget '"riscv64"' --command "hadrian/build -j --flavour=quickest"
diff --git a/README.md b/README.md
index 36b922b..49cad7a 100644
--- a/README.md
+++ b/README.md
@@ -104,6 +104,24 @@ It's trivial!
 $ nix-shell ~/ghc.nix/shell.nix --arg nixpkgs '(import <nixpkgs> {}).pkgsi686Linux'
 ```
 
+## Building a cross-compiler
+
+Cross-compiling in this section means: GHC is developed/built on one
+architecture (`--build`) to run on the same architecture (`--host`) and target
+another architecture (`--target`).
+
+E.g. develop GHC on *amd64*, run it on *amd64* and let the resulting GHC produce
+binaries for *riscv64*.
+
+The `crossTarget` argument defines the target. The string must be a supported
+architecture in `nixpkgs.pkgsCross`. When `crossTarget` is defined, all required
+environment variables and `configure_ghc` parameters are setup for building a
+cross-compiler.
+
+``` sh
+nix-shell --pure ghc.nix/shell.nix --arg withLlvm true --arg crossTarget '"riscv64"'
+```
+
 ## Cachix
 
 There is a Cachix cache ([ghc-nix](https://app.cachix.org/cache/ghc-nix)) which is filled by our CI. To use it, run the following command and follow the instructions:
diff --git a/ghc.nix b/ghc.nix
index d26b44e..2850a47 100644
--- a/ghc.nix
+++ b/ghc.nix
@@ -28,6 +28,7 @@ in
 , withDtrace ? (pkgsFor nixpkgs system).stdenv.isLinux
 , withGrind ? !((pkgsFor nixpkgs system).valgrind.meta.broken or false)
 , withEMSDK ? false                    # load emscripten for js-backend
+, crossTarget ? null # a `nixpkgs.pkgsCross` record, e.g. `riscv64`
 }:
 
 let
@@ -58,15 +59,20 @@ let
 
   pkgs-unstable =
     import nixpkgs-unstable { inherit system; overlays = [ overlay ]; };
+
+  pkgs-cross = if crossTarget != null then pkgs.pkgsCross.${crossTarget} else null;
 in
 
 with pkgs;
 
 let
   llvmForGhc =
+    let
+      ps = if crossTarget == null then pkgs else pkgs-cross.buildPackages;
+    in
     if lib.versionAtLeast version "9.1"
-    then llvm_10
-    else llvm_9;
+    then ps.llvm_12
+    else ps.llvm_9;
 
   stdenv =
     if useClang
@@ -176,23 +182,50 @@ hspkgs.shellFor rec {
   # In particular, this makes many tests fail because those warnings show up in test outputs too...
   # The solution is from: https://github.com/NixOS/nix/issues/318#issuecomment-52986702
   LOCALE_ARCHIVE = if stdenv.isLinux then "${glibcLocales}/lib/locale/locale-archive" else "";
-  CONFIGURE_ARGS = [
-    "--with-gmp-includes=${gmp.dev}/include"
-    "--with-gmp-libraries=${gmp}/lib"
-    "--with-curses-includes=${ncurses.dev}/include"
-    "--with-curses-libraries=${ncurses.out}/lib"
-  ] ++ lib.optionals withNuma [
-    "--with-libnuma-includes=${numactl}/include"
-    "--with-libnuma-libraries=${numactl}/lib"
-  ] ++ lib.optionals withDwarf [
-    "--with-libdw-includes=${elfutils.dev}/include"
-    "--with-libdw-libraries=${elfutils.out}/lib"
-    "--enable-dwarf-unwind"
-  ];
+
+  CONFIGURE_ARGS =
+    if crossTarget == null then
+      [
+        "--with-gmp-includes=${gmp.dev}/include"
+        "--with-gmp-libraries=${gmp}/lib"
+        "--with-curses-includes=${ncurses.dev}/include"
+        "--with-curses-libraries=${ncurses.out}/lib"
+      ] ++ lib.optionals withNuma [
+        "--with-libnuma-includes=${numactl}/include"
+        "--with-libnuma-libraries=${numactl}/lib"
+      ] ++ lib.optionals withDwarf [
+        "--with-libdw-includes=${elfutils.dev}/include"
+        "--with-libdw-libraries=${elfutils.out}/lib"
+        "--enable-dwarf-unwind"
+      ] else [
+      "--with-gmp-includes=${pkgs-cross.gmp.dev}/include"
+      "--with-gmp-libraries=${pkgs-cross.gmp}/lib"
+      "--with-curses-includes=${pkgs-cross.ncurses.dev}/include"
+      "--with-curses-libraries=${pkgs-cross.ncurses.out}/lib"
+      "--host=${stdenv.hostPlatform.config}"
+      "--target=${pkgs-cross.stdenv.hostPlatform.config}"
+    ];
+
+
+  targetDependentShellHook =
+    if crossTarget == null then
+      ''
+        export CC=${stdenv.cc}/bin/cc
+      '' else
+      let
+        prefix = pkgs-cross.stdenv.cc.targetPrefix;
+      in
+      ''
+        # somehow, CC gets overridden so we set it again here.
+        export CC=${pkgs-cross.stdenv.cc}/bin/${prefix}cc
+        export CXX=${pkgs-cross.stdenv.cc}/bin/${prefix}c++
+        export AR=${pkgs-cross.stdenv.cc.bintools.bintools}/bin/${prefix}ar
+        export RANLIB=${pkgs-cross.stdenv.cc.bintools.bintools}/bin/${prefix}ranlib
+        export NM=${pkgs-cross.stdenv.cc.bintools.bintools}/bin/${prefix}nm
+        export LD=${pkgs-cross.stdenv.cc.bintools}/bin/${prefix}ld
+      '';
 
   shellHook = ''
-    # somehow, CC gets overridden so we set it again here.
-    export CC=${stdenv.cc}/bin/cc
     export GHC=$NIX_GHC
     export GHCPKG=$NIX_GHCPKG
     export HAPPY=${happy}/bin/happy
@@ -216,8 +249,10 @@ hspkgs.shellFor rec {
 
     ${lib.optionalString withDocs "export FONTCONFIG_FILE=${fonts}"}
 
+    ${targetDependentShellHook}
     >&2 echo "Recommended ./configure arguments (found in \$CONFIGURE_ARGS:"
-    >&2 echo "or use the configure_ghc command):"
+    >&2 echo "or use the configure_ghc command - passing \$CONFIGURE_ARGS"
+    >&2 echo "itself to ./configure might not work):"
     >&2 echo ""
     >&2 echo "  ${lib.concatStringsSep "\n  " CONFIGURE_ARGS}"
   '';