diff --git a/wire/common.go b/wire/common.go
index b988c3df..673daa89 100644
--- a/wire/common.go
+++ b/wire/common.go
@@ -17,6 +17,11 @@ import (
 // Maximum payload size for a variable length integer.
 const MaxVarIntPayload = 9
 
+// errNonCanonicalVarInt is the common format string used for non-canonically
+// encoded variable length integer errors.
+var errNonCanonicalVarInt = "non-canonical varint %x - discriminant %x must " +
+	"encode a value greater than %x"
+
 // readElement reads the next sequence of bytes from r using little endian
 // depending on the concrete type of element pointed to.
 func readElement(r io.Reader, element interface{}) error {
@@ -336,6 +341,14 @@ func readVarInt(r io.Reader, pver uint32) (uint64, error) {
 		}
 		rv = binary.LittleEndian.Uint64(b[:])
 
+		// The encoding is not canonical if the value could have been
+		// encoded using fewer bytes.
+		min := uint64(0x100000000)
+		if rv < min {
+			return 0, messageError("readVarInt", fmt.Sprintf(
+				errNonCanonicalVarInt, rv, discriminant, min))
+		}
+
 	case 0xfe:
 		_, err := io.ReadFull(r, b[0:4])
 		if err != nil {
@@ -343,6 +356,14 @@ func readVarInt(r io.Reader, pver uint32) (uint64, error) {
 		}
 		rv = uint64(binary.LittleEndian.Uint32(b[:]))
 
+		// The encoding is not canonical if the value could have been
+		// encoded using fewer bytes.
+		min := uint64(0x10000)
+		if rv < min {
+			return 0, messageError("readVarInt", fmt.Sprintf(
+				errNonCanonicalVarInt, rv, discriminant, min))
+		}
+
 	case 0xfd:
 		_, err := io.ReadFull(r, b[0:2])
 		if err != nil {
@@ -350,6 +371,14 @@ func readVarInt(r io.Reader, pver uint32) (uint64, error) {
 		}
 		rv = uint64(binary.LittleEndian.Uint16(b[:]))
 
+		// The encoding is not canonical if the value could have been
+		// encoded using fewer bytes.
+		min := uint64(0xfd)
+		if rv < min {
+			return 0, messageError("readVarInt", fmt.Sprintf(
+				errNonCanonicalVarInt, rv, discriminant, min))
+		}
+
 	default:
 		rv = uint64(discriminant)
 	}
diff --git a/wire/common_test.go b/wire/common_test.go
index 3d955705..09df1c0c 100644
--- a/wire/common_test.go
+++ b/wire/common_test.go
@@ -354,6 +354,62 @@ func TestVarIntWireErrors(t *testing.T) {
 	}
 }
 
+// TestVarIntNonCanonical ensures variable length integers that are not encoded
+// canonically return the expected error.
+func TestVarIntNonCanonical(t *testing.T) {
+	pver := wire.ProtocolVersion
+
+	tests := []struct {
+		name string // Test name for easier identification
+		in   []byte // Value to decode
+		pver uint32 // Protocol version for wire encoding
+	}{
+		{
+			"0 encoded with 3 bytes", []byte{0xfd, 0x00, 0x00},
+			pver,
+		},
+		{
+			"max single-byte value encoded with 3 bytes",
+			[]byte{0xfd, 0xfc, 0x00}, pver,
+		},
+		{
+			"0 encoded with 5 bytes",
+			[]byte{0xfe, 0x00, 0x00, 0x00, 0x00}, pver,
+		},
+		{
+			"max three-byte value encoded with 5 bytes",
+			[]byte{0xfe, 0xff, 0xff, 0x00, 0x00}, pver,
+		},
+		{
+			"0 encoded with 9 bytes",
+			[]byte{0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
+			pver,
+		},
+		{
+			"max five-byte value encoded with 9 bytes",
+			[]byte{0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00},
+			pver,
+		},
+	}
+
+	t.Logf("Running %d tests", len(tests))
+	for i, test := range tests {
+		// Decode from wire format.
+		rbuf := bytes.NewReader(test.in)
+		val, err := wire.TstReadVarInt(rbuf, test.pver)
+		if _, ok := err.(*wire.MessageError); !ok {
+			t.Errorf("readVarInt #%d (%s) unexpected error %v", i,
+				test.name, err)
+			continue
+		}
+		if val != 0 {
+			t.Errorf("readVarInt #%d (%s)\n got: %d want: 0", i,
+				test.name, val)
+			continue
+		}
+	}
+}
+
 // TestVarIntWire tests the serialize size for variable length integers.
 func TestVarIntSerializeSize(t *testing.T) {
 	tests := []struct {
diff --git a/wire/msgversion.go b/wire/msgversion.go
index 7b6dbdc1..cdcbc302 100644
--- a/wire/msgversion.go
+++ b/wire/msgversion.go
@@ -18,7 +18,7 @@ import (
 const MaxUserAgentLen = 2000
 
 // DefaultUserAgent for wire in the stack
-const DefaultUserAgent = "/btcwire:0.2.0/"
+const DefaultUserAgent = "/btcwire:0.2.1/"
 
 // MsgVersion implements the Message interface and represents a bitcoin version
 // message.  It is used for a peer to advertise itself as soon as an outbound