diff --git a/include/stdplus/str/buf.hpp b/include/stdplus/str/buf.hpp
index 834f154..2725e21 100644
--- a/include/stdplus/str/buf.hpp
+++ b/include/stdplus/str/buf.hpp
@@ -24,8 +24,8 @@
     } inl;
     struct Dyn
     {
-        std::uint8_t
-            rsvd[offsetof(Inl, len) - sizeof(CharT*) - sizeof(std::size_t) * 2];
+        std::uint8_t rsvd[offsetof(Inl, len) + 1 - sizeof(CharT*) -
+                          sizeof(std::size_t) * 2];
         CharT* ptr;
         std::size_t cap;
         std::size_t len;