diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2eb2c3a..cf0d045 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -12,10 +12,16 @@ endif()
 
 # Compiler-specific optimizations
 # Note: -ffast-math is intentionally omitted — it breaks FINUFFT (IEEE-754 violations)
+# CI runners use x86-64-v3 (AVX2) for portability; local builds use native.
+if(DEFINED ENV{CI} AND "$ENV{CI}" STREQUAL "true")
+    set(MARCH_FLAG "-march=x86-64-v3")
+else()
+    set(MARCH_FLAG "-march=native -mtune=native")
+endif()
 if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-    set(CMAKE_CXX_FLAGS_RELEASE "-O3 -march=native -mtune=native")
+    set(CMAKE_CXX_FLAGS_RELEASE "-O3 ${MARCH_FLAG}")
 elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
-    set(CMAKE_CXX_FLAGS_RELEASE "-O3 -march=native -mtune=native")
+    set(CMAKE_CXX_FLAGS_RELEASE "-O3 ${MARCH_FLAG}")
 elseif(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
     set(CMAKE_CXX_FLAGS_RELEASE "/O2 /arch:AVX2")
 endif()
diff --git a/senpy/CMakeLists.txt b/senpy/CMakeLists.txt
index b1f9b8f..779cbe2 100644
--- a/senpy/CMakeLists.txt
+++ b/senpy/CMakeLists.txt
@@ -4,8 +4,12 @@ project(senpy)
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
-# Add optimization flags
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O3 -march=native")
+# Add optimization flags; CI runners use x86-64-v3 (AVX2) for portability.
+if(DEFINED ENV{CI} AND "$ENV{CI}" STREQUAL "true")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O3 -march=x86-64-v3")
+else()
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O3 -march=native")
+endif()
 
 # add ../cpp relative to this CMakeLists.txt
 set(CPP_DIR "${CMAKE_CURRENT_LIST_DIR}/../src")
diff --git a/senpy/setup.py b/senpy/setup.py
index 6694f87..1f894ef 100644
--- a/senpy/setup.py
+++ b/senpy/setup.py
@@ -107,7 +107,7 @@ def _copy_runtime_libraries(self):
         sources=sources,
         include_dirs=include_dirs,
         language='c++',
-        extra_compile_args=['-std=c++17', '-O3', '-march=native', '-DPYTHON'],
+        extra_compile_args=['-std=c++17', '-O3', '-march=x86-64-v3' if os.environ.get('CI') == 'true' else '-march=native', '-DPYTHON'],
         extra_link_args=[
             f'-L{finufft_lib_dir}',
             '-lfinufft',