diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7b0cb6f6..f46b1b6c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ Version 91:
 * Tidy up namespace qualifiers
 * Tidy up MSVC CMakeLists.txt
 * Optimize buffered_read_stream
+* constexpr in derived buffers
 
 WebSocket:
 
diff --git a/include/boost/beast/core/flat_static_buffer.hpp b/include/boost/beast/core/flat_static_buffer.hpp
index 489a512c..0f3ea3e0 100644
--- a/include/boost/beast/core/flat_static_buffer.hpp
+++ b/include/boost/beast/core/flat_static_buffer.hpp
@@ -235,6 +235,20 @@ public:
     {
         return *this;
     }
+
+    /// Return the maximum sum of the input and output sequence sizes.
+    std::size_t constexpr
+    max_size() const
+    {
+        return N;
+    }
+
+    /// Return the maximum sum of input and output sizes that can be held without an allocation.
+    std::size_t constexpr
+    capacity() const
+    {
+        return N;
+    }
 };
 
 } // beast
diff --git a/include/boost/beast/core/static_buffer.hpp b/include/boost/beast/core/static_buffer.hpp
index 568cf2fe..c6c5d0eb 100644
--- a/include/boost/beast/core/static_buffer.hpp
+++ b/include/boost/beast/core/static_buffer.hpp
@@ -216,6 +216,20 @@ public:
     {
         return *this;
     }
+
+    /// Return the maximum sum of the input and output sequence sizes.
+    std::size_t constexpr
+    max_size() const
+    {
+        return N;
+    }
+
+    /// Return the maximum sum of input and output sizes that can be held without an allocation.
+    std::size_t constexpr
+    capacity() const
+    {
+        return N;
+    }
 };
 
 } // beast