doc/news.rst           |  2 ++
 pyderasn.py            | 29 +++++++++++++++++++++++------
 tests/test_pyderasn.py |  4 ++--

diff --git a/doc/news.rst b/doc/news.rst
index 1c0dea1bd46d9c3b5a3333f0208a4f9961306bac997424ddea5779838c6e1107..1bbb50b6eda98d53f6e0a50c004d873ff096dc0770e126daf29c2c7530f5cd8e 100644
--- a/doc/news.rst
+++ b/doc/news.rst
@@ -6,6 +6,8 @@
 4.4
 ---
 * All errors are inherited from ASN1Error class
+* NumericString/PrintableString has allowable_chars property holding all
+  allowed characters
 
 .. _release4.3:
 
diff --git a/pyderasn.py b/pyderasn.py
index a13e1ac5c29842bfe994fe0a382651bb3169eaaa2d5dbccdfe967f77a1eff027..5d540b1b6e0e47ca69d8b6ab8dde6a4b2175ac484ca354739016abf56eabdb4d 100755
--- a/pyderasn.py
+++ b/pyderasn.py
@@ -555,6 +555,7 @@ from six import iterbytes
 from six import PY2
 from six import string_types
 from six import text_type
+from six import unichr as six_unichr
 from six.moves import xrange as six_xrange
 
 
@@ -3492,39 +3493,55 @@     encoding = "utf-8"
     asn1_type_name = "UTF8String"
 
 
-class NumericString(CommonString):
+class AllowableCharsMixin(object):
+    @property
+    def allowable_chars(self):
+        if PY2:
+            return self._allowable_chars
+        return set(six_unichr(c) for c in self._allowable_chars)
+
+
+class NumericString(AllowableCharsMixin, CommonString):
     """Numeric string
 
     Its value is properly sanitized: only ASCII digits with spaces can
     be stored.
+
+    >>> NumericString().allowable_chars
+    set(['3', '4', '7', '5', '1', '0', '8', '9', ' ', '6', '2'])
     """
     __slots__ = ()
     tag_default = tag_encode(18)
     encoding = "ascii"
     asn1_type_name = "NumericString"
-    allowable_chars = set(digits.encode("ascii") + b" ")
+    _allowable_chars = set(digits.encode("ascii") + b" ")
 
     def _value_sanitize(self, value):
         value = super(NumericString, self)._value_sanitize(value)
-        if not set(value) <= self.allowable_chars:
+        if not set(value) <= self._allowable_chars:
             raise DecodeError("non-numeric value")
         return value
 
 
-class PrintableString(CommonString):
+class PrintableString(AllowableCharsMixin, CommonString):
     """Printable string
 
     Its value is properly sanitized: see X.680 41.4 table 10.
+
+    >>> PrintableString().allowable_chars
+    >>> set([' ', "'", ..., 'z'])
     """
     __slots__ = ()
     tag_default = tag_encode(19)
     encoding = "ascii"
     asn1_type_name = "PrintableString"
-    allowable_chars = set((ascii_letters + digits + " '()+,-./:=?").encode("ascii"))
+    _allowable_chars = set(
+        (ascii_letters + digits + " '()+,-./:=?").encode("ascii")
+    )
 
     def _value_sanitize(self, value):
         value = super(PrintableString, self)._value_sanitize(value)
-        if not set(value) <= self.allowable_chars:
+        if not set(value) <= self._allowable_chars:
             raise DecodeError("non-printable value")
         return value
 
diff --git a/tests/test_pyderasn.py b/tests/test_pyderasn.py
index 43ed60780cb7ab4e2f28db1d9f1c8bd5dfdec0c93577fc805c79c00edda43130..1c23bc05bb593fcdbec8275cb5c477369dfc35b72a9f429c2c88013dc5f93ad5 100644
--- a/tests/test_pyderasn.py
+++ b/tests/test_pyderasn.py
@@ -5869,10 +5869,10 @@         seq = Seq()
         seq["erste"] = PrintableString("test")
         self.assertSequenceEqual(seq.encode(), hexdec("3006130474657374"))
         # Asterisk is actually not allowable
-        PrintableString.allowable_chars |= set(b"*")
+        PrintableString._allowable_chars |= set(b"*")
         seq["erste"] = PrintableString("test*")
         self.assertSequenceEqual(seq.encode(), hexdec("30071305746573742a"))
-        PrintableString.allowable_chars -= set(b"*")
+        PrintableString._allowable_chars -= set(b"*")
 
         class Seq(Sequence):
             schema = (