diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 4d1a37ad7..4a07670c7 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -2590,12 +2590,13 @@ JSON_HEDLEY_DIAGNOSTIC_POP
              class NumberUnsignedType, class NumberFloatType,              \
              template<typename> class AllocatorType,                       \
              template<typename, typename = void> class JSONSerializer,     \
-             class BinaryType>
+             class BinaryType,                                             \
+             class CustomBaseClass>
 
 #define NLOHMANN_BASIC_JSON_TPL                                            \
     basic_json<ObjectType, ArrayType, StringType, BooleanType,             \
     NumberIntegerType, NumberUnsignedType, NumberFloatType,                \
-    AllocatorType, JSONSerializer, BinaryType>
+    AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>
 
 // Macros to simplify conversion from/to types
 
@@ -3389,7 +3390,8 @@ NLOHMANN_JSON_NAMESPACE_END
     template<typename U> class AllocatorType = std::allocator,
     template<typename T, typename SFINAE = void> class JSONSerializer =
     adl_serializer,
-    class BinaryType = std::vector<std::uint8_t>>
+    class BinaryType = std::vector<std::uint8_t>, // cppcheck-suppress syntaxError
+    class CustomBaseClass = void>
     class basic_json;
 
     /// @brief JSON Pointer defines a string syntax for identifying a specific value within a JSON document
@@ -13673,6 +13675,38 @@ NLOHMANN_JSON_NAMESPACE_END
 
 // #include <nlohmann/detail/iterators/primitive_iterator.hpp>
 
+// #include <nlohmann/detail/json_custom_base_class.hpp>
+
+
+#include <type_traits> // conditional, is_same
+
+namespace nlohmann
+{
+namespace detail
+{
+
+/*!
+@brief Default base class of the @ref basic_json class.
+
+So that the correct implementation of the copy / move ctors / assign operators
+of @ref basic_json does not require complex case distinctions
+(no base class / custom base class used as customization point),
+@ref basic_json always has a base class.
+By default, this class is used because it is empty and thus has no effect
+on the behavior of @ref basic_json.
+*/
+struct json_default_base {};
+
+template<class T>
+using json_base_class = typename std::conditional <
+                        std::is_same<T, void>::value,
+                        json_default_base,
+                        T
+                        >::type;
+
+}  // namespace detail
+}  // namespace nlohmann
+
 // #include <nlohmann/detail/json_pointer.hpp>
 //     __ _____ _____ _____
 //  __|  |   __|     |   | |  JSON for Modern C++
@@ -19271,6 +19305,7 @@ The invariants are checked by member function assert_invariant().
 */
 NLOHMANN_BASIC_JSON_TPL_DECLARATION
 class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-special-member-functions)
+    : public ::nlohmann::detail::json_base_class<CustomBaseClass>
 {
   private:
     template<detail::value_t> friend struct detail::external_constructor;
@@ -19297,6 +19332,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// workaround type for MSVC
     using basic_json_t = NLOHMANN_BASIC_JSON_TPL;
+    using json_base_class_t = ::nlohmann::detail::json_base_class<CustomBaseClass>;
 
   JSON_PRIVATE_UNLESS_TESTED:
     // convenience aliases for types residing in namespace detail;
@@ -20310,7 +20346,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @brief copy constructor
     /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     basic_json(const basic_json& other)
-        : m_type(other.m_type)
+        : json_base_class_t(other),
+          m_type(other.m_type)
     {
         // check of passed value is valid
         other.assert_invariant();
@@ -20378,11 +20415,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @brief move constructor
     /// @sa https://json.nlohmann.me/api/basic_json/basic_json/
     basic_json(basic_json&& other) noexcept
-        : m_type(std::move(other.m_type)),
+        : json_base_class_t(std::move(other)),
+          m_type(std::move(other.m_type)),
           m_value(std::move(other.m_value))
     {
         // check that passed value is valid
-        other.assert_invariant(false);
+        other.assert_invariant(false); // NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
 
         // invalidate payload
         other.m_type = value_t::null;
@@ -20398,7 +20436,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         std::is_nothrow_move_constructible<value_t>::value&&
         std::is_nothrow_move_assignable<value_t>::value&&
         std::is_nothrow_move_constructible<json_value>::value&&
-        std::is_nothrow_move_assignable<json_value>::value
+        std::is_nothrow_move_assignable<json_value>::value&&
+        std::is_nothrow_move_assignable<json_base_class_t>::value
     )
     {
         // check that passed value is valid
@@ -20407,6 +20446,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         using std::swap;
         swap(m_type, other.m_type);
         swap(m_value, other.m_value);
+        json_base_class_t::operator=(std::move(other));
 
         set_parents();
         assert_invariant();
diff --git a/single_include/nlohmann/json_fwd.hpp b/single_include/nlohmann/json_fwd.hpp
index 83c21f857..98070dfc9 100644
--- a/single_include/nlohmann/json_fwd.hpp
+++ b/single_include/nlohmann/json_fwd.hpp
@@ -147,7 +147,8 @@ template<template<typename U, typename V, typename... Args> class ObjectType =
          template<typename U> class AllocatorType = std::allocator,
          template<typename T, typename SFINAE = void> class JSONSerializer =
          adl_serializer,
-         class BinaryType = std::vector<std::uint8_t>>
+         class BinaryType = std::vector<std::uint8_t>, // cppcheck-suppress syntaxError
+         class CustomBaseClass = void>
 class basic_json;
 
 /// @brief JSON Pointer defines a string syntax for identifying a specific value within a JSON document