diff --git a/pyopenjtalk/htsengine.pyx b/pyopenjtalk/htsengine.pyx
index 868c07a..cdc6018 100644
--- a/pyopenjtalk/htsengine.pyx
+++ b/pyopenjtalk/htsengine.pyx
@@ -117,9 +117,9 @@ cdef class HTSEngine:
         cdef size_t nsamples = HTS_Engine_get_nsamples(self.engine)
         cdef np.ndarray[np.float64_t, ndim=1] speech = np.zeros([nsamples], dtype=np.float64)
         cdef double[::1] speech_view = speech
-        cdef size_t index
+        cdef int index
         for index in prange(nsamples, nogil=True):
-            speech_view[index] = HTS_Engine_get_generated_speech(self.engine, index)
+            speech_view[index] = HTS_Engine_get_generated_speech(self.engine, <size_t>index)
         return speech
 
     cpdef inline str get_fullcontext_label_format(self):
diff --git a/pyopenjtalk/openjtalk.pyx b/pyopenjtalk/openjtalk.pyx
index 1ef7923..4f37112 100644
--- a/pyopenjtalk/openjtalk.pyx
+++ b/pyopenjtalk/openjtalk.pyx
@@ -1,6 +1,6 @@
 # coding: utf-8
 # cython: language_level=3
-# cython: boundscheck=False, wraparound=False
+# cython: boundscheck=False, wraparound=True
 # cython: c_string_type=unicode, c_string_encoding=ascii, cdivision=True
 
 from libc.stdint cimport uint8_t
diff --git a/setup.py b/setup.py
index 971a08b..8a6ddcc 100644
--- a/setup.py
+++ b/setup.py
@@ -1,6 +1,7 @@
 import os
 import subprocess
 import sys
+import platform
 from distutils.errors import DistutilsExecError
 from distutils.spawn import spawn
 from distutils.version import LooseVersion
@@ -70,6 +71,24 @@ def build_extensions(self):
     if not os.path.exists(join("pyopenjtalk", "openjtalk" + ext)):
         raise RuntimeError("Cython is required to generate C++ code")
 
+# make openmp available
+system = platform.system()
+if system == "Windows":
+    extra_compile_args = []
+    extra_link_args = ['/openmp']
+elif system == "Linux":
+    extra_compile_args = ['-fopenmp']
+    extra_link_args = ['-fopenmp']
+elif system == "Darwin":
+    os.system("brew install llvm libomp")
+    os.system("brew install clang-omp")
+    # os.environ["CPP"] = "/usr/local/opt/llvm/bin/clang"
+    extra_compile_args = ["-Xpreprocessor", "-fopenmp"]
+    extra_link_args = ["-Xpreprocessor", "-fopenmp"]
+else:
+    extra_compile_args = ['-fopenmp']
+    extra_link_args = ['-fopenmp']
+
 
 # Workaround for `distutils.spawn` problem on Windows python < 3.9
 # See details: [bpo-39763: distutils.spawn now uses subprocess (GH-18743)]
@@ -180,8 +199,8 @@ def escape_macros(macros):
         name="pyopenjtalk.openjtalk",
         sources=[join("pyopenjtalk", "openjtalk" + ext)] + all_src,
         include_dirs=[np.get_include()] + include_dirs,
-        extra_compile_args=['-fopenmp'],
-        extra_link_args=['-fopenmp'],
+        extra_compile_args=extra_compile_args,
+        extra_link_args=extra_link_args,
         language="c++",
         define_macros=custom_define_macros(
             [
@@ -204,8 +223,8 @@ def escape_macros(macros):
         name="pyopenjtalk.htsengine",
         sources=[join("pyopenjtalk", "htsengine" + ext)] + all_htsengine_src,
         include_dirs=[np.get_include(), join(htsengine_src_top, "include")],
-        extra_compile_args=['-fopenmp'],
-        extra_link_args=['-fopenmp'],
+        extra_compile_args=extra_compile_args,
+        extra_link_args=extra_link_args,
         libraries=["winmm"] if platform_is_windows else [],
         language="c++",
         define_macros=custom_define_macros(