diff --git a/tests/__init__.py b/tests/__init__.py
index 643ebd9..17805e0 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -105,6 +105,18 @@ class ArchiveTest (unittest.TestCase):
             shutil.rmtree(tmpdir)
 
 
+def needs_os (name):
+    """Decorator skipping test if given program is not available."""
+    def check_prog (f):
+        def newfunc (*args, **kwargs):
+            if os.name != name:
+                raise nose.SkipTest("operating system %s not found" % name)
+            return f(*args, **kwargs)
+        newfunc.func_name = f.func_name
+        return newfunc
+    return check_prog
+
+
 def needs_program (program):
     """Decorator skipping test if given program is not available."""
     def check_prog (f):
diff --git a/tests/test_archives.py b/tests/test_archives.py
index bb72507..3e0cc8e 100644
--- a/tests/test_archives.py
+++ b/tests/test_archives.py
@@ -213,6 +213,7 @@ class TestArchives (ArchiveTest):
         self.program = 'arj'
         self.archive_commands('t.arj')
 
+    @needs_os('posix')
     @needs_program('ar')
     def test_ar (self):
         self.program = 'ar'
diff --git a/tests/test_foo_archives.py b/tests/test_foo_archives.py
index 4d85307..885c3b6 100644
--- a/tests/test_foo_archives.py
+++ b/tests/test_foo_archives.py
@@ -243,6 +243,7 @@ class TestArchives (ArchiveTest):
         self.program = 'arj'
         self.archive_commands('t.arj.foo', format="arj")
 
+    @needs_os('posix')
     @needs_program('file')
     @needs_program('ar')
     def test_ar (self):