diff --git a/multiaddr/multiaddr.py b/multiaddr/multiaddr.py
index 653beb3..d91536d 100644
--- a/multiaddr/multiaddr.py
+++ b/multiaddr/multiaddr.py
@@ -38,13 +38,9 @@ def __init__(self, string_addr=None, bytes_addr=None):
 
         Only one of string_addr or bytes_addr may be set
         """
-        if string_addr is not None and bytes_addr is not None:
-            raise ValueError(
-                "Only one of 'string_addr' or 'bytes_addr' may be set")
-
-        if string_addr is not None:
+        if string_addr is not None and bytes_addr is None:
             self._bytes = string_to_bytes(string_addr)
-        elif bytes_addr is not None:
+        elif bytes_addr is not None and string_addr is None:
             self._bytes = bytes_addr
         else:
             raise ValueError("Invalid address type, must be bytes or str")
@@ -105,8 +101,9 @@ def decapsulate(self, other):
         """
         s1 = str(self)
         s2 = str(other)
-        idx = s1.rindex(s2)
-        if idx < 0:
+        try:
+            idx = s1.rindex(s2)
+        except ValueError:
             # if multiaddr not contained, returns a copy
             return copy(self)
         try:
diff --git a/tests/test_multiaddr.py b/tests/test_multiaddr.py
index 2e3ad84..9abf4f7 100755
--- a/tests/test_multiaddr.py
+++ b/tests/test_multiaddr.py
@@ -188,6 +188,11 @@ def test_encapsulate():
     decapsulated_2 = decapsulated.decapsulate(m4)
     assert str(decapsulated_2) == ""
 
+    m5 = Multiaddr("/ip6/::1")
+    decapsulated_3 = decapsulated.decapsulate(m5)
+
+    assert str(decapsulated_3) == "/ip4/127.0.0.1/udp/1234"
+
 
 def assert_value_for_proto(multi, proto, expected):
     assert multi.value_for_protocol(proto) == expected
@@ -218,3 +223,54 @@ def test_get_value():
     assert_value_for_proto(a, P_IP4, "0.0.0.0")
     assert_value_for_proto(a, P_UDP, "12345")
     assert_value_for_proto(a, P_UTP, "")
+
+
+def test_bad_initialization_no_params():
+    with pytest.raises(ValueError):
+        Multiaddr()
+
+
+def test_bad_initialization_too_many_params():
+    with pytest.raises(ValueError):
+        Multiaddr("/ip4/0.0.0.0", string_to_bytes("/ip4/0.0.0.0"))
+
+
+def test_get_value_too_many_fields_protocol(monkeypatch):
+    """
+    This test patches the Multiaddr's string representation to return
+    an invalid string in order to test that value_for_protocol properly
+    throws a ValueError.  This avoids some of the error checking in
+    the constructor and is easier to patch, thus the actual values
+    that the constructor specifies is ignored by the test.
+    """
+    monkeypatch.setattr("multiaddr.multiaddr.Multiaddr.__str__",
+                        lambda ignore: '/udp/1234/5678')
+    a = Multiaddr("/ip4/127.0.0.1/udp/1234")
+    with pytest.raises(ValueError):
+        a.value_for_protocol(P_UDP)
+
+
+def test_multi_addr_str_corruption():
+    a = Multiaddr("/ip4/127.0.0.1/udp/1234")
+    a._bytes = b"047047047"
+
+    with pytest.raises(ValueError):
+        str(a)
+
+
+def test_decapsulate_corrupted_bytes(monkeypatch):
+    def raiseException(self, other):
+        raise Exception
+
+    a = Multiaddr("/ip4/127.0.0.1/udp/1234")
+    u = Multiaddr("/udp/1234")
+    monkeypatch.setattr("multiaddr.multiaddr.Multiaddr.__init__",
+                        raiseException)
+
+    with pytest.raises(ValueError):
+        a.decapsulate(u)
+
+
+def test__repr():
+    a = Multiaddr("/ip4/127.0.0.1/udp/1234")
+    assert(repr(a) == "<Multiaddr %s>" % str(a))