diff --git a/samples/monster_generated.h b/samples/monster_generated.h
index fdbac0fcc..cdde13c4a 100644
--- a/samples/monster_generated.h
+++ b/samples/monster_generated.h
@@ -77,8 +77,8 @@ struct EquipmentUnion {
   EquipmentUnion(EquipmentUnion&& u) FLATBUFFERS_NOEXCEPT :
     type(Equipment_NONE), value(nullptr)
     { std::swap(type, u.type); std::swap(value, u.value); }
-  EquipmentUnion(const EquipmentUnion &);
-  EquipmentUnion &operator=(const EquipmentUnion &);
+  EquipmentUnion(const EquipmentUnion &) { assert(false); }
+  EquipmentUnion &operator=(const EquipmentUnion &) { assert(false); return *this; }
   EquipmentUnion &operator=(EquipmentUnion &&u) FLATBUFFERS_NOEXCEPT
     { std::swap(type, u.type); std::swap(value, u.value); return *this; }
   ~EquipmentUnion() { Reset(); }
diff --git a/src/idl_gen_cpp.cpp b/src/idl_gen_cpp.cpp
index d821eb402..1bfadf21a 100644
--- a/src/idl_gen_cpp.cpp
+++ b/src/idl_gen_cpp.cpp
@@ -687,8 +687,8 @@ class CppGenerator : public BaseGenerator {
       code_ += "  {{NAME}}Union({{NAME}}Union&& u) FLATBUFFERS_NOEXCEPT :";
       code_ += "    type({{NONE}}), value(nullptr)";
       code_ += "    { std::swap(type, u.type); std::swap(value, u.value); }";
-      code_ += "  {{NAME}}Union(const {{NAME}}Union &);";
-      code_ += "  {{NAME}}Union &operator=(const {{NAME}}Union &);";
+      code_ += "  {{NAME}}Union(const {{NAME}}Union &) { assert(false); }";
+      code_ += "  {{NAME}}Union &operator=(const {{NAME}}Union &) { assert(false); return *this; }";
       code_ += "  {{NAME}}Union &operator=({{NAME}}Union &&u) FLATBUFFERS_NOEXCEPT";
       code_ += "    { std::swap(type, u.type); std::swap(value, u.value); return *this; }";
       code_ += "  ~{{NAME}}Union() { Reset(); }";
diff --git a/tests/monster_test_generated.h b/tests/monster_test_generated.h
index 08970f942..647367a96 100644
--- a/tests/monster_test_generated.h
+++ b/tests/monster_test_generated.h
@@ -108,8 +108,8 @@ struct AnyUnion {
   AnyUnion(AnyUnion&& u) FLATBUFFERS_NOEXCEPT :
     type(Any_NONE), value(nullptr)
     { std::swap(type, u.type); std::swap(value, u.value); }
-  AnyUnion(const AnyUnion &);
-  AnyUnion &operator=(const AnyUnion &);
+  AnyUnion(const AnyUnion &) { assert(false); }
+  AnyUnion &operator=(const AnyUnion &) { assert(false); return *this; }
   AnyUnion &operator=(AnyUnion &&u) FLATBUFFERS_NOEXCEPT
     { std::swap(type, u.type); std::swap(value, u.value); return *this; }
   ~AnyUnion() { Reset(); }
diff --git a/tests/union_vector/union_vector_generated.h b/tests/union_vector/union_vector_generated.h
index 24046bc5d..88f4f368d 100644
--- a/tests/union_vector/union_vector_generated.h
+++ b/tests/union_vector/union_vector_generated.h
@@ -55,8 +55,8 @@ struct CharacterUnion {
   CharacterUnion(CharacterUnion&& u) FLATBUFFERS_NOEXCEPT :
     type(Character_NONE), value(nullptr)
     { std::swap(type, u.type); std::swap(value, u.value); }
-  CharacterUnion(const CharacterUnion &);
-  CharacterUnion &operator=(const CharacterUnion &);
+  CharacterUnion(const CharacterUnion &) { assert(false); }
+  CharacterUnion &operator=(const CharacterUnion &) { assert(false); return *this; }
   CharacterUnion &operator=(CharacterUnion &&u) FLATBUFFERS_NOEXCEPT
     { std::swap(type, u.type); std::swap(value, u.value); return *this; }
   ~CharacterUnion() { Reset(); }