diff --git a/src/cryptobox/core/blockdevice.py b/src/cryptobox/core/blockdevice.py
index 4dc20e1..01561e0 100644
--- a/src/cryptobox/core/blockdevice.py
+++ b/src/cryptobox/core/blockdevice.py
@@ -741,8 +741,12 @@ class Blockdevice:
         output += "\tflags:\t\t"
         for funcname in [ func for func in dir(self)
                 if func.startswith("is_") and callable(getattr(self, func))]:
-            if getattr(self, funcname)():
-                output += "%s " % funcname[3:]
+            try:
+                if getattr(self, funcname)():
+                    output += "%s " % funcname[3:]
+            except TypeError:
+                # skip tests that need arguments (e.g. "is_parent_of")
+                pass
         output += "\n"
         return output
 
@@ -1003,7 +1007,11 @@ if __name__ == '__main__':
         for check in flag_checker:
             show("List of '%s' devices:" % check[3:])
             for device in blocks:
-                if getattr(device, check)():
-                    show("\t%s" % device)
+                try:
+                    if getattr(device, check)():
+                        show("\t%s" % device)
+                except TypeError:
+                    # ignore tests that need a second argument
+                    pass
             show()