diff --git a/CHANGELOG.md b/CHANGELOG.md
index c490bfea..50d2dfd8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@ Version 286:
 * Refactor static_buffer
 * Refactor flat_buffer
 * Refactor flat_static_buffer
+* Fix missing include in sha1.hpp
 
 API Changes:
 
diff --git a/include/boost/beast/core/detail/sha1.hpp b/include/boost/beast/core/detail/sha1.hpp
index c4c8d5e3..26612d0d 100644
--- a/include/boost/beast/core/detail/sha1.hpp
+++ b/include/boost/beast/core/detail/sha1.hpp
@@ -12,6 +12,7 @@
 
 #include <boost/beast/core/detail/config.hpp>
 #include <cstdint>
+#include <cstddef>
 
 // Based on https://github.com/vog/sha1
 /*