diff --git a/marshal.go b/marshal.go
index c07b042..03d45e4 100644
--- a/marshal.go
+++ b/marshal.go
@@ -47,6 +47,8 @@ func Marshal(in interface{}) (interface{}, error) {
 			return marshalTimestamp(v), nil
 		case bson.RegEx:
 			return marshalRegex(v), nil
+		case bson.Decimal128:
+			return marshalDecimal128(v), nil
 		case string, int, int64, bool, float64, uint8, uint32:
 			return v, nil
 		default:
@@ -111,3 +113,9 @@ func marshalRegex(in bson.RegEx) map[string]interface{} {
 		"$options": in.Options,
 	}
 }
+
+func marshalDecimal128(in bson.Decimal128) map[string]interface{} {
+	return map[string]interface{}{
+		"$decimal128": in.String(),
+	}
+}