diff --git a/src/lib/gcrypt/Hash.hxx b/src/lib/gcrypt/Hash.hxx
index a1a52a644..84bba84d9 100644
--- a/src/lib/gcrypt/Hash.hxx
+++ b/src/lib/gcrypt/Hash.hxx
@@ -36,7 +36,7 @@
 
 namespace Gcrypt {
 
-template<int algo, size_t size>
+template<int algo, std::size_t size>
 [[gnu::pure]]
 auto
 Hash(std::span<const std::byte> input) noexcept