diff --git a/README.md b/README.md
index 2990a3cdb..72717c808 100644
--- a/README.md
+++ b/README.md
@@ -45,6 +45,7 @@ A [sub-package](https://godoc.org/github.com/globalsign/mgo/bson) that implement
 * Gracefully recover from a temporarily unreachable server ([details](https://github.com/globalsign/mgo/pull/69))
 * Use JSON tags when no explicit BSON are tags set ([details](https://github.com/globalsign/mgo/pull/91))
 * Support [$changeStream](https://docs.mongodb.com/manual/changeStreams/) tailing on 3.6+ ([details](https://github.com/globalsign/mgo/pull/97))
+* Fix deadlock in cluster synchronisation ([details](https://github.com/globalsign/mgo/issues/120))
 
 ---
 
@@ -55,11 +56,13 @@ A [sub-package](https://godoc.org/github.com/globalsign/mgo/bson) that implement
 * @carter2000
 * @cezarsa
 * @drichelson
+* @dvic
 * @eaglerayp
 * @feliixx
 * @fmpwizard
 * @idy
 * @jameinel
+* @KJTsanaktsidis
 * @gazoon
 * @mapete94
 * @peterdeka
diff --git a/bson/bson_test.go b/bson/bson_test.go
index ebb8b96bd..406ede6ae 100644
--- a/bson/bson_test.go
+++ b/bson/bson_test.go
@@ -607,6 +607,8 @@ func (s *S) TestMarshalOneWayItems(c *C) {
 // --------------------------------------------------------------------------
 // One-way unmarshaling tests.
 
+type intAlias int
+
 var unmarshalItems = []testItemType{
 	// Field is private.  Should not attempt to unmarshal it.
 	{&struct{ priv byte }{},
@@ -661,6 +663,14 @@ var unmarshalItems = []testItemType{
 	// Decode a doc within a doc in to a slice within a doc; shouldn't error
 	{&struct{ Foo []string }{},
 		"\x03\x66\x6f\x6f\x00\x05\x00\x00\x00\x00"},
+
+	// int key maps
+	{map[int]string{10: "s"},
+		"\x0210\x00\x02\x00\x00\x00s\x00"},
+
+	//// event if type is alias to int
+	{map[intAlias]string{10: "s"},
+		"\x0210\x00\x02\x00\x00\x00s\x00"},
 }
 
 func (s *S) TestUnmarshalOneWayItems(c *C) {
@@ -738,11 +748,6 @@ var unmarshalErrorItems = []unmarshalErrorType{
 		"\x10name\x00\x08\x00\x00\x00",
 		"Duplicated key 'name' in struct bson_test.structWithDupKeys"},
 
-	// Non-string map key.
-	{map[int]interface{}{},
-		"\x10name\x00\x08\x00\x00\x00",
-		"BSON map must have string keys. Got: map\\[int\\]interface \\{\\}"},
-
 	{nil,
 		"\xEEname\x00",
 		"Unknown element kind \\(0xEE\\)"},
@@ -758,6 +763,11 @@ var unmarshalErrorItems = []unmarshalErrorType{
 	{nil,
 		"\x08\x62\x00\x02",
 		"encoded boolean must be 1 or 0, found 2"},
+
+	// Non-string and not numeric map key.
+	{map[bool]interface{}{true: 1},
+		"\x10true\x00\x01\x00\x00\x00",
+		"BSON map must have string or decimal keys. Got: map\\[bool\\]interface \\{\\}"},
 }
 
 func (s *S) TestUnmarshalErrorItems(c *C) {
@@ -1161,8 +1171,8 @@ type inlineBadKeyMap struct {
 	M map[int]int `bson:",inline"`
 }
 type inlineUnexported struct {
-	M          map[string]interface{} `bson:",inline"`
-	unexported `bson:",inline"`
+	M map[string]interface{} `bson:",inline"`
+	unexported               `bson:",inline"`
 }
 type unexported struct {
 	A int
@@ -1219,11 +1229,11 @@ func (s ifaceSlice) GetBSON() (interface{}, error) {
 
 type (
 	MyString string
-	MyBytes  []byte
-	MyBool   bool
-	MyD      []bson.DocElem
-	MyRawD   []bson.RawDocElem
-	MyM      map[string]interface{}
+	MyBytes []byte
+	MyBool bool
+	MyD []bson.DocElem
+	MyRawD []bson.RawDocElem
+	MyM map[string]interface{}
 )
 
 var (
diff --git a/bson/decode.go b/bson/decode.go
index e71eac23f..658856add 100644
--- a/bson/decode.go
+++ b/bson/decode.go
@@ -176,9 +176,6 @@ func (d *decoder) readDocTo(out reflect.Value) {
 	switch outk {
 	case reflect.Map:
 		keyType = outt.Key()
-		if keyType.Kind() != reflect.String {
-			panic("BSON map must have string keys. Got: " + outt.String())
-		}
 		if keyType != typeString {
 			convertKey = true
 		}
@@ -240,7 +237,42 @@ func (d *decoder) readDocTo(out reflect.Value) {
 			if d.readElemTo(e, kind) {
 				k := reflect.ValueOf(name)
 				if convertKey {
-					k = k.Convert(keyType)
+					mapKeyType := out.Type().Key()
+					mapKeyKind := mapKeyType.Kind()
+
+					switch mapKeyKind {
+					case reflect.Int:
+						fallthrough
+					case reflect.Int8:
+						fallthrough
+					case reflect.Int16:
+						fallthrough
+					case reflect.Int32:
+						fallthrough
+					case reflect.Int64:
+						fallthrough
+					case reflect.Uint:
+						fallthrough
+					case reflect.Uint8:
+						fallthrough
+					case reflect.Uint16:
+						fallthrough
+					case reflect.Uint32:
+						fallthrough
+					case reflect.Uint64:
+						fallthrough
+					case reflect.Float32:
+						fallthrough
+					case reflect.Float64:
+						parsed := d.parseMapKeyAsFloat(k, mapKeyKind)
+						k = reflect.ValueOf(parsed)
+					case reflect.String:
+						mapKeyType = keyType
+					default:
+						panic("BSON map must have string or decimal keys. Got: " + outt.String())
+					}
+
+					k = k.Convert(mapKeyType)
 				}
 				out.SetMapIndex(k, e)
 			}
@@ -276,6 +308,16 @@ func (d *decoder) readDocTo(out reflect.Value) {
 	d.docType = docType
 }
 
+func (decoder) parseMapKeyAsFloat(k reflect.Value, mapKeyKind reflect.Kind) float64 {
+	parsed, err := strconv.ParseFloat(k.String(), 64)
+	if err != nil {
+		panic("Map key is defined to be a decimal type (" + mapKeyKind.String() + ") but got error " +
+			err.Error())
+	}
+
+	return parsed
+}
+
 func (d *decoder) readArrayDocTo(out reflect.Value) {
 	end := int(d.readInt32())
 	end += d.i - 4
diff --git a/bson/encode.go b/bson/encode.go
index 5d5f452b0..7e0b84d77 100644
--- a/bson/encode.go
+++ b/bson/encode.go
@@ -203,7 +203,7 @@ func (e *encoder) addDoc(v reflect.Value) {
 
 func (e *encoder) addMap(v reflect.Value) {
 	for _, k := range v.MapKeys() {
-		e.addElem(k.String(), v.MapIndex(k), false)
+		e.addElem(fmt.Sprint(k), v.MapIndex(k), false)
 	}
 }