diff --git a/CHANGELOG.md b/CHANGELOG.md
index 63134933..059d3677 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ API Changes:
 * Remove header_parser
 * Add verb to on_request for parsers
 * Refactor prepare
+* Protect basic_fields special members
 
 --------------------------------------------------------------------------------
 
diff --git a/include/beast/http/fields.hpp b/include/beast/http/fields.hpp
index 6c0b339d..dbba0b34 100644
--- a/include/beast/http/fields.hpp
+++ b/include/beast/http/fields.hpp
@@ -71,15 +71,11 @@ public:
         off_t len;
     };
 
-public:
-    /// The type of allocator used.
-    using allocator_type = Allocator;
-
-    /// A constant iterator to the field sequence.
-    class const_iterator;
-
-    /// A constant iterator to the field sequence.
-    using iterator = const_iterator;
+protected:
+    //
+    // These are for `header`
+    //
+    friend class fields_test;
 
     /// Destructor
     ~basic_fields();
@@ -152,6 +148,16 @@ public:
 #endif
     basic_fields& operator=(basic_fields<OtherAlloc> const&);
 
+public:
+    /// The type of allocator used.
+    using allocator_type = Allocator;
+
+    /// A constant iterator to the field sequence.
+    class const_iterator;
+
+    /// A constant iterator to the field sequence.
+    using iterator = const_iterator;
+
     /// Return a copy of the allocator associated with the container.
     allocator_type
     get_allocator() const
@@ -304,7 +310,10 @@ public:
     swap(basic_fields<Alloc>& lhs, basic_fields<Alloc>& rhs);
 
 protected:
-    // for header
+    //
+    // for `header
+    //
+
     string_view method_impl() const;
     string_view target_impl() const;
     string_view reason_impl() const;
diff --git a/test/http/message.cpp b/test/http/message.cpp
index 17bb1273..1f766ab9 100644
--- a/test/http/message.cpp
+++ b/test/http/message.cpp
@@ -114,14 +114,14 @@ public:
         }
 
         {
-            fields h;
+            header<true, fields> h;
             h.insert("User-Agent", "test");
             message<true, one_arg_body, fields> m{Arg1{}, h};
             BEAST_EXPECT(h["User-Agent"] == "test");
             BEAST_EXPECT(m["User-Agent"] == "test");
         }
         {
-            fields h;
+            header<true, fields> h;
             h.insert("User-Agent", "test");
             message<true, one_arg_body, fields> m{Arg1{}, std::move(h)};
             BEAST_EXPECT(! h.exists("User-Agent"));