diff --git a/.github/workflows/cmake.yml b/.github/workflows/cmake.yml
new file mode 100644
index 0000000..57b93ed
--- /dev/null
+++ b/.github/workflows/cmake.yml
@@ -0,0 +1,21 @@
+name: CMake
+
+on:
+  push:
+  pull_request:
+
+env:
+  # Customize the CMake build type here (Release, Debug, RelWithDebInfo, etc.)
+  BUILD_TYPE: Release
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        submodules: true
+
+    - name: Build
+      run: ci/build.sh
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 36510d2..8a74978 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,4 +8,6 @@ include_directories(
   .
 )
 
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror")
+
 add_subdirectory(examples)
diff --git a/ci/build.sh b/ci/build.sh
new file mode 100755
index 0000000..de0c0fa
--- /dev/null
+++ b/ci/build.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+
+cmake -S . -B build
+cmake --build build -j
diff --git a/examples/c/character.cmake b/examples/c/character.cmake
index bcbea53..9b9bf2e 100644
--- a/examples/c/character.cmake
+++ b/examples/c/character.cmake
@@ -1,3 +1,6 @@
 add_executable(
   character
-  character.c)
+  character.c
+)
+
+target_link_libraries(character m)
diff --git a/examples/c/geometry.cmake b/examples/c/geometry.cmake
index 109983c..eb8ec0a 100644
--- a/examples/c/geometry.cmake
+++ b/examples/c/geometry.cmake
@@ -1,3 +1,6 @@
 add_executable(
   geometry
-  geometry.c)
+  geometry.c
+)
+
+target_link_libraries(geometry m)
diff --git a/examples/c/logo.c b/examples/c/logo.c
index 2ae6595..c225288 100644
--- a/examples/c/logo.c
+++ b/examples/c/logo.c
@@ -322,7 +322,7 @@ int main() {
   }
 
   uint64_t end = time_ms();
-  printf("render time: %llums", end - start);
+  printf("render time: %lums", end - start);
 
 
 
diff --git a/examples/c/logo.cmake b/examples/c/logo.cmake
index 44eb065..5ddcc64 100644
--- a/examples/c/logo.cmake
+++ b/examples/c/logo.cmake
@@ -2,3 +2,5 @@ add_executable(
   logo
   logo.c
 )
+
+target_link_libraries(logo m)
diff --git a/pretty-poly.h b/pretty-poly.h
index 7890a6c..647b3c8 100644
--- a/pretty-poly.h
+++ b/pretty-poly.h
@@ -260,7 +260,7 @@ pp_rect_t pp_polygon_bounds(pp_poly_t *p) {
 // buffer that each tile is rendered into before callback
 // allocate one extra byte to allow a small optimization in the row renderer
 const uint32_t tile_buffer_size = PP_TILE_BUFFER_SIZE;
-uint8_t tile_buffer[tile_buffer_size + 1];
+uint8_t tile_buffer[PP_TILE_BUFFER_SIZE + 1];
 
 // polygon node buffer handles at most 16 line intersections per scanline
 // is this enough for cjk/emoji? (requires a 2kB buffer)