diff --git a/setup.py b/setup.py
index e1b7899..a7ed278 100644
--- a/setup.py
+++ b/setup.py
@@ -279,17 +279,19 @@ def run(self):
         _pari_c = os.path.join('cypari', '_pari.c')
         cythonize([_pari_pyx],
                   compiler_directives={'language_level':2})
-        with open('_pari.c', 'w') as outfile:
-            with open(_pari_c) as infile:
-                for line in infile.readlines():
-                    if line.find('pycore') >= 0:
-                        outfile.write(
-                            '  #undef long\n%s'
-                            '  #define long long long\n' %line)
-                    else:
-                        outfile.write(line)
-        os.unlink(_pari_c)
-        os.rename('_pari.c', _pari_c)
+        if sys.platform == 'win32':
+            # patch _pari.c to deal with #define long long long
+            with open('_pari.c', 'w') as outfile:
+                with open(_pari_c) as infile:
+                    for line in infile.readlines():
+                        if line.find('pycore') >= 0:
+                            outfile.write(
+                                '  #undef long\n%s'
+                                '  #define long long long\n' %line)
+                        else:
+                            outfile.write(line)
+            os.unlink(_pari_c)
+            os.rename('_pari.c', _pari_c)
         build_ext.run(self)
 
 class CyPariSourceDist(sdist):