diff --git a/src/detail/probe-encoder.hpp b/src/detail/probe-encoder.hpp
index bde8a87..58bcb44 100644
--- a/src/detail/probe-encoder.hpp
+++ b/src/detail/probe-encoder.hpp
@@ -39,7 +39,8 @@
 Block
 encodeDataContent(const std::vector<Name>& identifiers,
                   optional<size_t> maxSuffixLength = nullopt,
-                  optional<std::vector<std::shared_ptr<security::Certificate>>> redirectionItems = nullopt);
+                  std::vector<std::shared_ptr<security::Certificate>> redirectionItems =
+                          std::vector<std::shared_ptr<security::Certificate>>());
 
 std::multimap<std::string, std::string>
 decodeApplicationParameters(const Block& block);