diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d5b1bae23a..81456ae17c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -4,46 +4,39 @@ name: CI
 on:
   pull_request:
   push:
-    branches: ["ghc-8.10"]
+    branches: ["ghc-9.0"]
 
 jobs:
   cabal:
-    name: ${{ matrix.os }} / ghc ${{ matrix.ghc }}
+    name: ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest]
-        cabal: ["3.2"]
-        ghc:
-          - "8.10.1"
-          - "8.10.2"
-
+        os: [ubuntu-latest]  # TODO: add macOS/Windows
     steps:
     - uses: actions/checkout@v2
-      if: github.event.action == 'opened' || github.event.action == 'synchronize' || github.event.ref == 'refs/heads/ghc-8.10'
-
-    - uses: actions/setup-haskell@v1.1.4
-      id: setup-haskell-cabal
-      name: Setup Haskell
-      with:
-        ghc-version: ${{ matrix.ghc }}
-        cabal-version: ${{ matrix.cabal }}
-
-    - name: Freeze
+    - name: Install GHC/Cabal
       run: |
-        cabal freeze
-
-    - uses: actions/cache@v1
-      name: Cache ~/.cabal/store
+        mkdir -p $HOME/.ghcup/bin
+        curl -Lf "https://downloads.haskell.org/~ghcup/x86_64-linux-ghcup" > $HOME/.ghcup/bin/ghcup
+        chmod u+x $HOME/.ghcup/bin/ghcup
+        export PATH="$HOME/.cabal/bin:$HOME/.ghcup/bin:$PATH"
+        echo "$HOME/.cabal/bin" >> $GITHUB_PATH
+        echo "$HOME/.ghcup/bin" >> $GITHUB_PATH
+        ghcup install ghc 9.0.0.20201227
+        ghcup install cabal 3.4.0.0-rc4
+        ghcup set ghc 9.0.0.20201227
+        ghcup set cabal 3.4.0.0-rc4
+    - name: Cache
+      uses: actions/cache@v1
       with:
-        path: ${{ steps.setup-haskell-cabal.outputs.cabal-store }}
-        key: ${{ runner.os }}-${{ matrix.ghc }}-${{ hashFiles('cabal.project.freeze') }}
-
-    - name: Build
+        path: ~/.cabal
+        key: ${{ runner.os }}
+    - name: Install dependencies
       run: |
-        cabal configure --enable-tests --enable-benchmarks --test-show-details=direct
-        cabal build all
-
-    - name: Test
-      run: |
-        cabal test all
+        cabal update
+        cabal build all --only-dependencies --enable-tests --enable-benchmarks
+    - name: Build
+      run: cabal build all --enable-tests --enable-benchmarks
+    - name: Run tests
+      run: cabal test all
diff --git a/cabal.project b/cabal.project
index 7330a775e9..2525070aa8 100644
--- a/cabal.project
+++ b/cabal.project
@@ -3,5 +3,12 @@ packages: ./
           ./haddock-library
           ./haddock-test
 
+with-compiler: ghc-9.0
+
+allow-newer:
+  ghc-paths:Cabal,
+  *:base,
+  *:ghc-prim
+
 -- Pinning the index-state helps to make reasonably CI deterministic
-index-state: 2020-12-08T20:13:44Z
+index-state: 2021-01-24T12:09:34Z
diff --git a/haddock-api/haddock-api.cabal b/haddock-api/haddock-api.cabal
index 93f59c1f32..f3dbe2e2c4 100644
--- a/haddock-api/haddock-api.cabal
+++ b/haddock-api/haddock-api.cabal
@@ -189,6 +189,7 @@ test-suite spec
                , containers
                , deepseq
                , directory
+               , exceptions
                , filepath
                , ghc-boot
                , transformers