diff --git a/src/OpenSSL/crypto.py b/src/OpenSSL/crypto.py
index d555083..715e1ae 100644
--- a/src/OpenSSL/crypto.py
+++ b/src/OpenSSL/crypto.py
@@ -695,11 +695,11 @@
             nid = _lib.OBJ_obj2nid(fname)
             name = _lib.OBJ_nid2sn(nid)
 
-            result.append((
-                _ffi.string(name),
-                _ffi.string(
-                    _lib.ASN1_STRING_data(fval),
-                    _lib.ASN1_STRING_length(fval))))
+            # ffi.string does not handle strings containing NULL bytes
+            # (which may have been generated by old, broken software)
+            value = _ffi.buffer(_lib.ASN1_STRING_data(fval),
+                                _lib.ASN1_STRING_length(fval))[:]
+            result.append((_ffi.string(name), value))
 
         return result