diff --git a/router/handshake.go b/router/handshake.go
index d3fd8424..128bbcb0 100644
--- a/router/handshake.go
+++ b/router/handshake.go
@@ -12,11 +12,11 @@ type FieldValidator struct {
 	err    error
 }
 
-func NewFieldValidator(fields map[string]string) FieldValidator {
-	return FieldValidator{fields, nil}
+func NewFieldValidator(fields map[string]string) *FieldValidator {
+	return &FieldValidator{fields, nil}
 }
 
-func (fv FieldValidator) Value(fieldName string) (string, error) {
+func (fv *FieldValidator) Value(fieldName string) (string, error) {
 	if fv.err != nil {
 		return "", fv.err
 	}
@@ -28,7 +28,7 @@ func (fv FieldValidator) Value(fieldName string) (string, error) {
 	return val, nil
 }
 
-func (fv FieldValidator) CheckEqual(fieldName, expectedValue string) error {
+func (fv *FieldValidator) CheckEqual(fieldName, expectedValue string) error {
 	val, err := fv.Value(fieldName)
 	if err != nil {
 		return err
@@ -40,7 +40,7 @@ func (fv FieldValidator) CheckEqual(fieldName, expectedValue string) error {
 	return nil
 }
 
-func (fv FieldValidator) Err() error {
+func (fv *FieldValidator) Err() error {
 	return fv.err
 }
 
@@ -146,7 +146,7 @@ func (conn *LocalConnection) handshakeSendRecv(localConnID uint64, usingPassword
 	fv.CheckEqual("Protocol", Protocol)
 	fv.CheckEqual("ProtocolVersion", versionStr)
 	fv.CheckEqual("PeerNameFlavour", PeerNameFlavour)
-	return &fv, private, nil
+	return fv, private, nil
 }
 
 func (conn *LocalConnection) setRemote(toPeer *Peer) error {
diff --git a/router/handshake_test.go b/router/handshake_test.go
new file mode 100644
index 00000000..e7306cfb
--- /dev/null
+++ b/router/handshake_test.go
@@ -0,0 +1,29 @@
+package router
+
+import (
+	wt "github.com/weaveworks/weave/testing"
+	"testing"
+)
+
+func TestFieldValidator(t *testing.T) {
+	testMap := map[string]string{"a": "a"}
+
+	fv := NewFieldValidator(testMap)
+	val, err := fv.Value("a")
+	wt.AssertNoErr(t, err)
+	wt.AssertNoErr(t, fv.Err())
+	wt.AssertEqualString(t, val, "a", "a")
+	_, err = fv.Value("x")
+	wt.AssertFalse(t, err == nil || fv.Err() == nil, "Expected error")
+	_, err = fv.Value("a")
+	wt.AssertFalse(t, err == nil || fv.Err() == nil, "Previous error should be retained")
+
+	fv = NewFieldValidator(testMap)
+	err = fv.CheckEqual("a", "a")
+	wt.AssertNoErr(t, err)
+	wt.AssertNoErr(t, fv.Err())
+	err = fv.CheckEqual("a", "b")
+	wt.AssertFalse(t, err == nil || fv.Err() == nil, "Expected error")
+	err = fv.CheckEqual("a", "a")
+	wt.AssertFalse(t, err == nil || fv.Err() == nil, "Previous error should be retained")
+}