diff --git a/bson/bsoncodec.go b/bson/bsoncodec.go
index e0369a1111..08e3d4b862 100644
--- a/bson/bsoncodec.go
+++ b/bson/bsoncodec.go
@@ -171,8 +171,8 @@ type decodeAdapter struct {
 var _ ValueDecoder = decodeAdapter{}
 var _ typeDecoder = decodeAdapter{}
 
-func decodeTypeOrValueWithInfo(vd ValueDecoder, td typeDecoder, dc DecodeContext, vr ValueReader, t reflect.Type, convert bool) (reflect.Value, error) {
-	if td != nil {
+func decodeTypeOrValueWithInfo(vd ValueDecoder, dc DecodeContext, vr ValueReader, t reflect.Type, convert bool) (reflect.Value, error) {
+	if td := vd.(typeDecoder); td != nil {
 		val, err := td.decodeType(dc, vr, t)
 		if err == nil && convert && val.Type() != t {
 			// This conversion step is necessary for slices and maps. If a user declares variables like:
diff --git a/bson/default_value_decoders.go b/bson/default_value_decoders.go
index 56331da9a8..50f7fc7cb9 100644
--- a/bson/default_value_decoders.go
+++ b/bson/default_value_decoders.go
@@ -135,7 +135,6 @@ func dDecodeValue(dc DecodeContext, vr ValueReader, val reflect.Value) error {
 	if err != nil {
 		return err
 	}
-	tEmptyTypeDecoder, _ := decoder.(typeDecoder)
 
 	// Use the elements in the provided value if it's non nil. Otherwise, allocate a new D instance.
 	var elems D
@@ -155,7 +154,7 @@ func dDecodeValue(dc DecodeContext, vr ValueReader, val reflect.Value) error {
 		}
 
 		// Pass false for convert because we don't need to call reflect.Value.Convert for tEmpty.
-		elem, err := decodeTypeOrValueWithInfo(decoder, tEmptyTypeDecoder, dc, elemVr, tEmpty, false)
+		elem, err := decodeTypeOrValueWithInfo(decoder, dc, elemVr, tEmpty, false)
 		if err != nil {
 			return err
 		}
@@ -1274,7 +1273,6 @@ func decodeDefault(dc DecodeContext, vr ValueReader, val reflect.Value) ([]refle
 	if err != nil {
 		return nil, err
 	}
-	eTypeDecoder, _ := decoder.(typeDecoder)
 
 	idx := 0
 	for {
@@ -1286,7 +1284,7 @@ func decodeDefault(dc DecodeContext, vr ValueReader, val reflect.Value) ([]refle
 			return nil, err
 		}
 
-		elem, err := decodeTypeOrValueWithInfo(decoder, eTypeDecoder, dc, vr, eType, true)
+		elem, err := decodeTypeOrValueWithInfo(decoder, dc, vr, eType, true)
 		if err != nil {
 			return nil, newDecodeError(strconv.Itoa(idx), err)
 		}
diff --git a/bson/empty_interface_codec.go b/bson/empty_interface_codec.go
index 59754ec6b5..b8314a873f 100644
--- a/bson/empty_interface_codec.go
+++ b/bson/empty_interface_codec.go
@@ -99,7 +99,7 @@ func (eic emptyInterfaceCodec) decodeType(dc DecodeContext, vr ValueReader, t re
 		return emptyValue, err
 	}
 
-	elem, err := decodeTypeOrValueWithInfo(decoder, decoder.(typeDecoder), dc, vr, rtype, true)
+	elem, err := decodeTypeOrValueWithInfo(decoder, dc, vr, rtype, true)
 	if err != nil {
 		return emptyValue, err
 	}
diff --git a/bson/map_codec.go b/bson/map_codec.go
index bfa77ca0d8..5f6963ed26 100644
--- a/bson/map_codec.go
+++ b/bson/map_codec.go
@@ -160,7 +160,6 @@ func (mc *mapCodec) DecodeValue(dc DecodeContext, vr ValueReader, val reflect.Va
 	if err != nil {
 		return err
 	}
-	eTypeDecoder, _ := decoder.(typeDecoder)
 
 	if eType == tEmpty {
 		dc.ancestor = val.Type()
@@ -182,7 +181,7 @@ func (mc *mapCodec) DecodeValue(dc DecodeContext, vr ValueReader, val reflect.Va
 			return err
 		}
 
-		elem, err := decodeTypeOrValueWithInfo(decoder, eTypeDecoder, dc, vr, eType, true)
+		elem, err := decodeTypeOrValueWithInfo(decoder, dc, vr, eType, true)
 		if err != nil {
 			return newDecodeError(key, err)
 		}