diff --git a/CMakeLists.txt b/CMakeLists.txt
index 06a95b8d..72f43a27 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -26,19 +26,12 @@ if(EMSCRIPTEN)
 elseif(MSVC)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /EHsc /utf-8 /O2")
 else()
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexceptions")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexceptions -O2")
 
     # disable -Wshorten-64-to-32 for apple
     if(APPLE)
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-shorten-64-to-32")
     endif()
-
-    # if android, use -Os
-    if(ANDROID)
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Os")
-    else()
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O2")
-    endif()
 endif()
 
 include_directories(${CMAKE_CURRENT_LIST_DIR}/include)
diff --git a/build_android.sh b/build_android.sh
index 7c407b97..f4d9e99f 100644
--- a/build_android.sh
+++ b/build_android.sh
@@ -10,6 +10,7 @@ cmake \
     -DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_HOME/build/cmake/android.toolchain.cmake \
     -DANDROID_ABI=$1 \
     -DANDROID_PLATFORM=android-22 \
+    -DANDROID_STL=c++_shared \
     ../../.. \
     -DPK_BUILD_SHARED_LIB=ON -DPK_USE_CJSON=ON -DPK_USE_BOX2D=ON \
     -DCMAKE_BUILD_TYPE=Release