diff --git a/tftypes/value_msgpack.go b/tftypes/value_msgpack.go
index d2fa8a36..105d0b5e 100644
--- a/tftypes/value_msgpack.go
+++ b/tftypes/value_msgpack.go
@@ -552,6 +552,7 @@ func marshalMsgPackObject(val Value, typ Type, p *AttributePath, enc *msgpack.En
 		return unexpectedValueTypeError(p, o, val.value, typ)
 	}
 	types := typ.(Object).AttributeTypes
+	optionalTypes := typ.(Object).OptionalAttributes
 	keys := make([]string, 0, len(types))
 	for k := range types {
 		keys = append(keys, k)
@@ -565,6 +566,9 @@ func marshalMsgPackObject(val Value, typ Type, p *AttributePath, enc *msgpack.En
 		ty := types[k]
 		v, ok := o[k]
 		if !ok {
+			if _, isOptional := optionalTypes[k]; isOptional {
+				continue
+			}
 			return p.WithAttributeName(k).NewErrorf("no value set")
 		}
 		err := marshalMsgPack(NewValue(String, k), String, p.WithAttributeName(k), enc)