diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 254b1a9d..80ba83af 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,7 +27,10 @@ jobs:
     - name: build (LLVM ${{ matrix.llvm_version }})
       # Run the build manually in `nix develop` to keep non-outputs around
       run: |
-        nix develop .#oid-llvm${{ matrix.llvm_version }} --command cmake -B build -G Ninja -DWITH_FLAKY_TESTS=Off -DFORCE_BOOST_STATIC=Off
+        nix develop .#oid-llvm${{ matrix.llvm_version }} --command cmake -B build -G Ninja \
+          -DWITH_FLAKY_TESTS=Off \
+          -DFORCE_BOOST_STATIC=Off \
+          -DCODE_COVERAGE=On
         nix develop .#oid-llvm${{ matrix.llvm_version }} --command ninja -C build
     - name: test (LLVM ${{ matrix.llvm_version }})
       env:
@@ -46,9 +49,29 @@ jobs:
           --repeat until-pass:3 \
           --exclude-from-file ../../.github/workflows/tests_failing_under_nix.txt \
           --output-junit results.xml
+
+    - name: upload coverage
+      continue-on-error: true
+      uses: coverallsapp/github-action@v2
+      with:
+        flag-name: run-${{ join(matrix.*, '-') }}
+        parallel: true
+
     - name: upload results
       uses: actions/upload-artifact@v4
       if: success() || failure()
       with:
         name: test-results-${{ matrix.llvm_version }}
         path: build/test/results.xml
+
+  finalise-coverage:
+    needs: build-test
+    if: ${{ always() }}
+    runs-on: ubuntu-latest
+    steps:
+    - name: finalise coverage
+      uses: coverallsapp/github-action@v2
+      with:
+        parallel-finished: true
+        carryforward: "run-15,run-16"
+
diff --git a/flake.nix b/flake.nix
index 577a490c..6e031bab 100644
--- a/flake.nix
+++ b/flake.nix
@@ -108,7 +108,7 @@
           in
           pkgs.mkShell.override { stdenv = llvmPackages.stdenv; } {
             inputsFrom = [ self.packages.${system}."oid-llvm${toString llvmVersion}" ];
-            buildInputs = [ ];
+            buildInputs = with pkgs; [ lcov ];
           };
       in
       {