diff --git a/src/cryptobox/tests/test.core.blockdevice.py b/src/cryptobox/tests/test.core.blockdevice.py
index b0d2ff3..f65e323 100755
--- a/src/cryptobox/tests/test.core.blockdevice.py
+++ b/src/cryptobox/tests/test.core.blockdevice.py
@@ -31,6 +31,14 @@ from cryptobox.core.exceptions import CBInternalError
 import os
 
 
+# different commonly available block devices - used for testing major/minor
+COMMON_DEV_INFOS = [
+        ('/sys/block/hda/hda1', '/dev/hda1', '/dev/hda', (3,1)),
+        ('/sys/block/sda/sda1', '/dev/sda1', '/dev/sda', (8,1)),
+        ('/sys/block/ubda/ubda', '/dev/ubda1', '/dev/ubda', (98,1)),
+        ('/sys/block/ubdb/ubdb1', '/dev/ubdb1', '/dev/ubdb', (98,17)),
+        ]
+
 class CoreBlockDevice(CommonTestClass):
     """All unittests for cryptoboxtools
     """
@@ -39,7 +47,14 @@ class CoreBlockDevice(CommonTestClass):
         """check the find_major_minor_of_device function
         """
         func = blockdevice.get_blockdevice
-        self.assertTrue(func('/dev/ram0').devnum == (1, 0))
+        # check if any of the common block devices is available
+        blockdevice_found = False
+        for sys_dir, dev_node, parent, major_minor in COMMON_DEV_INFOS:
+            if os.path.isdir(sys_dir):
+                self.assertTrue(func(dev_node).devnum == major_minor)
+                blockdevice_found = True
+        # we assume, that we found at least one blockdevice
+        self.assertTrue(blockdevice_found)
         self.assertTrue(func("/dev/nothere") is None)
 
 
@@ -47,13 +62,20 @@ class CoreBlockDevice(CommonTestClass):
         """check the is_part_of_blockdevice function
         """
         get_device = lambda devname: blockdevice.get_blockdevice(devname)
-        func = lambda parent, child: get_device(parent).is_parent_of(get_device(child))
+        func = lambda parent, child: get_device(parent) and get_device(parent).is_parent_of(get_device(child))
         func_raw = lambda parent: get_device(parent).is_parent_of
         self.assertTrue(func(self.blockdevice, self.device))
         self.assertFalse(func(self.blockdevice, self.blockdevice))
         self.assertFalse(func(self.device, self.blockdevice))
         self.assertFalse(func(self.device, self.device))
         self.assertFalse(func(self.blockdevice, "/dev/hde1"))
+        # check if any of the common block devices is available
+        blockdevice_found = False
+        for sys_dir, dev_node, parent, major_minor in COMMON_DEV_INFOS:
+            if os.path.isdir(sys_dir):
+                self.assertFalse(func(dev_node, parent))
+                self.assertTrue(func(parent, dev_node))
+                blockdevice_found = True
         self.assertFalse(func("ram0", "ram1"))
         self.assertFalse(func_raw(self.blockdevice)(None))
         self.assertRaises(CBInternalError, func_raw(self.blockdevice), "")