diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..25746a6
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,39 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  build:
+    name: PHP ${{ matrix.php }} ${{ matrix.ts }} on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-24.04, macos-15]
+        php: ['8.4', '8.5']
+        ts: [nts, zts]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          tools: none
+        env:
+          phpts: ${{ matrix.ts == 'zts' && 'ts' || 'nts' }}
+
+      - name: Build
+        run: |
+          phpize
+          ./configure --enable-rasterize
+          make -j"$(nproc 2>/dev/null || sysctl -n hw.ncpu)"
+
+      - name: Load
+        run: |
+          php -n -d extension="$PWD/modules/rasterize.so" -r 'exit(extension_loaded("rasterize") ? 0 : 1);'
+          php -n -d extension="$PWD/modules/rasterize.so" --ri rasterize
diff --git a/README.md b/README.md
index 56949fb..6429bec 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,7 @@
 # ext-rasterize
 
+[![CI](https://img.shields.io/github/actions/workflow/status/php-io-extensions/rasterize/ci.yml?style=flat-square&label=CI)](https://github.com/php-io-extensions/rasterize/actions/workflows/ci.yml)
+
 Shapes into coverage spans in C. `RasterScanner` holds a clip and an edge mode
 and answers paths, ellipses, rings and one-pixel polylines as span bytes, ready
 for a pixel store to paint. Geometry only: it never touches a pixel. Written