diff --git a/go/logic/migrator.go b/go/logic/migrator.go
index 85dae29..291a490 100644
--- a/go/logic/migrator.go
+++ b/go/logic/migrator.go
@@ -741,7 +741,7 @@ func (this *Migrator) initiateInspector() (err error) {
 		this.migrationContext.Log.Infof("Master found to be %+v", *this.migrationContext.ApplierConnectionConfig.ImpliedKey)
 	} else {
 		// Forced master host.
-		key, err := mysql.ParseRawInstanceKeyLoose(this.migrationContext.AssumeMasterHostname)
+		key, err := mysql.ParseInstanceKey(this.migrationContext.AssumeMasterHostname)
 		if err != nil {
 			return err
 		}
diff --git a/go/mysql/instance_key.go b/go/mysql/instance_key.go
index 67284d9..eb108d8 100644
--- a/go/mysql/instance_key.go
+++ b/go/mysql/instance_key.go
@@ -7,6 +7,7 @@ package mysql
 
 import (
 	"fmt"
+	"regexp"
 	"strconv"
 	"strings"
 )
@@ -15,6 +16,13 @@ const (
 	DefaultInstancePort = 3306
 )
 
+var (
+	ipv4HostPortRegexp = regexp.MustCompile("^([^:]+):([0-9]+)$")
+	ipv4HostRegexp     = regexp.MustCompile("^([^:]+)$")
+	ipv6HostPortRegexp = regexp.MustCompile("^\\[([:0-9a-fA-F]+)\\]:([0-9]+)$") // e.g. [2001:db8:1f70::999:de8:7648:6e8]:3308
+	ipv6HostRegexp     = regexp.MustCompile("^([:0-9a-fA-F]+)$")                // e.g. 2001:db8:1f70::999:de8:7648:6e8
+)
+
 // InstanceKey is an instance indicator, identified by hostname and port
 type InstanceKey struct {
 	Hostname string
@@ -25,25 +33,35 @@ const detachHint = "//"
 
 // ParseInstanceKey will parse an InstanceKey from a string representation such as 127.0.0.1:3306
 func NewRawInstanceKey(hostPort string) (*InstanceKey, error) {
-	tokens := strings.SplitN(hostPort, ":", 2)
-	if len(tokens) != 2 {
-		return nil, fmt.Errorf("Cannot parse InstanceKey from %s. Expected format is host:port", hostPort)
+	hostname := ""
+	port := ""
+	if submatch := ipv4HostPortRegexp.FindStringSubmatch(hostPort); len(submatch) > 0 {
+		hostname = submatch[1]
+		port = submatch[2]
+	} else if submatch := ipv4HostRegexp.FindStringSubmatch(hostPort); len(submatch) > 0 {
+		hostname = submatch[1]
+	} else if submatch := ipv6HostPortRegexp.FindStringSubmatch(hostPort); len(submatch) > 0 {
+		hostname = submatch[1]
+		port = submatch[2]
+	} else if submatch := ipv6HostRegexp.FindStringSubmatch(hostPort); len(submatch) > 0 {
+		hostname = submatch[1]
+	} else {
+		return nil, fmt.Errorf("Cannot parse address: %s", hostPort)
 	}
-	instanceKey := &InstanceKey{Hostname: tokens[0]}
-	var err error
-	if instanceKey.Port, err = strconv.Atoi(tokens[1]); err != nil {
-		return instanceKey, fmt.Errorf("Invalid port: %s", tokens[1])
+	instanceKey := &InstanceKey{Hostname: hostname, Port: DefaultInstancePort}
+	if port != "" {
+		var err error
+		if instanceKey.Port, err = strconv.Atoi(port); err != nil {
+			return instanceKey, fmt.Errorf("Invalid port: %s", port)
+		}
 	}
 
 	return instanceKey, nil
 }
 
-// ParseRawInstanceKeyLoose will parse an InstanceKey from a string representation such as 127.0.0.1:3306.
+// ParseInstanceKey will parse an InstanceKey from a string representation such as 127.0.0.1:3306.
 // The port part is optional; there will be no name resolve
-func ParseRawInstanceKeyLoose(hostPort string) (*InstanceKey, error) {
-	if !strings.Contains(hostPort, ":") {
-		return &InstanceKey{Hostname: hostPort, Port: DefaultInstancePort}, nil
-	}
+func ParseInstanceKey(hostPort string) (*InstanceKey, error) {
 	return NewRawInstanceKey(hostPort)
 }
 
diff --git a/go/mysql/instance_key_map.go b/go/mysql/instance_key_map.go
index d0900ef..1065fb9 100644
--- a/go/mysql/instance_key_map.go
+++ b/go/mysql/instance_key_map.go
@@ -92,7 +92,7 @@ func (this *InstanceKeyMap) ReadCommaDelimitedList(list string) error {
 	}
 	tokens := strings.Split(list, ",")
 	for _, token := range tokens {
-		key, err := ParseRawInstanceKeyLoose(token)
+		key, err := ParseInstanceKey(token)
 		if err != nil {
 			return err
 		}
diff --git a/go/mysql/instance_key_test.go b/go/mysql/instance_key_test.go
new file mode 100644
index 0000000..778a5b3
--- /dev/null
+++ b/go/mysql/instance_key_test.go
@@ -0,0 +1,74 @@
+/*
+   Copyright 2016 GitHub Inc.
+	 See https://github.com/github/gh-ost/blob/master/LICENSE
+*/
+
+package mysql
+
+import (
+	"testing"
+
+	"github.com/outbrain/golib/log"
+	test "github.com/outbrain/golib/tests"
+)
+
+func init() {
+	log.SetLevel(log.ERROR)
+}
+
+func TestParseInstanceKey(t *testing.T) {
+	{
+		key, err := ParseInstanceKey("myhost:1234")
+		test.S(t).ExpectNil(err)
+		test.S(t).ExpectEquals(key.Hostname, "myhost")
+		test.S(t).ExpectEquals(key.Port, 1234)
+	}
+	{
+		key, err := ParseInstanceKey("myhost")
+		test.S(t).ExpectNil(err)
+		test.S(t).ExpectEquals(key.Hostname, "myhost")
+		test.S(t).ExpectEquals(key.Port, 3306)
+	}
+	{
+		key, err := ParseInstanceKey("10.0.0.3:3307")
+		test.S(t).ExpectNil(err)
+		test.S(t).ExpectEquals(key.Hostname, "10.0.0.3")
+		test.S(t).ExpectEquals(key.Port, 3307)
+	}
+	{
+		key, err := ParseInstanceKey("10.0.0.3")
+		test.S(t).ExpectNil(err)
+		test.S(t).ExpectEquals(key.Hostname, "10.0.0.3")
+		test.S(t).ExpectEquals(key.Port, 3306)
+	}
+	{
+		key, err := ParseInstanceKey("[2001:db8:1f70::999:de8:7648:6e8]:3308")
+		test.S(t).ExpectNil(err)
+		test.S(t).ExpectEquals(key.Hostname, "2001:db8:1f70::999:de8:7648:6e8")
+		test.S(t).ExpectEquals(key.Port, 3308)
+	}
+	{
+		key, err := ParseInstanceKey("::1")
+		test.S(t).ExpectNil(err)
+		test.S(t).ExpectEquals(key.Hostname, "::1")
+		test.S(t).ExpectEquals(key.Port, 3306)
+	}
+	{
+		key, err := ParseInstanceKey("0:0:0:0:0:0:0:0")
+		test.S(t).ExpectNil(err)
+		test.S(t).ExpectEquals(key.Hostname, "0:0:0:0:0:0:0:0")
+		test.S(t).ExpectEquals(key.Port, 3306)
+	}
+	{
+		_, err := ParseInstanceKey("[2001:xxxx:1f70::999:de8:7648:6e8]:3308")
+		test.S(t).ExpectNotNil(err)
+	}
+	{
+		_, err := ParseInstanceKey("10.0.0.4:")
+		test.S(t).ExpectNotNil(err)
+	}
+	{
+		_, err := ParseInstanceKey("10.0.0.4:5.6.7")
+		test.S(t).ExpectNotNil(err)
+	}
+}