diff --git a/src/blackmisc/json.h b/src/blackmisc/json.h
index 7300a4df0..e90c1add6 100644
--- a/src/blackmisc/json.h
+++ b/src/blackmisc/json.h
@@ -29,10 +29,6 @@
 #include <type_traits>
 #include <utility>
 
-#if QT_VERSION >= 0x50701
-#define BLACK_USE_LATIN1_JSON_KEYS
-#endif
-
 class QDateTime;
 class QPixmap;
 class QStringList;
@@ -53,17 +49,8 @@ namespace BlackMisc
         //! Implicit constructor.
         Q_DECL_CONSTEXPR CExplicitLatin1String(QLatin1String s) : m_latin1(s) {}
 
-#ifdef BLACK_USE_LATIN1_JSON_KEYS
-        //! Type usable as key in QJsonObject.
-        Q_DECL_CONSTEXPR auto toJsonKey() const { return *this; }
         //! Implicit conversion.
         Q_DECL_CONSTEXPR operator QLatin1String() const { return m_latin1; }
-#else
-        //! Type usable as key in QJsonObject.
-        QString toJsonKey() const { return m_latin1; }
-        //! Implicit conversion.
-        operator QString() const { return m_latin1; }
-#endif
     };
 }
 
@@ -357,7 +344,7 @@ namespace BlackMisc
                 auto meta = introspect<Derived>().without(MetaFlags<DisabledForJson>());
                 meta.forEachMember([ &, this ](auto member)
                 {
-                    json << std::make_pair(CExplicitLatin1String(member.latin1Name()).toJsonKey(), std::cref(member.in(*this->derived())));
+                    json << std::make_pair(CExplicitLatin1String(member.latin1Name()), std::cref(member.in(*this->derived())));
                 });
                 return Json::appendJsonObject(json, baseToJson(static_cast<const TBaseOfT<Derived> *>(derived())));
             }
diff --git a/src/blackmisc/simulation/aircraftmodel.cpp b/src/blackmisc/simulation/aircraftmodel.cpp
index b3580c8ce..1dd602c0d 100644
--- a/src/blackmisc/simulation/aircraftmodel.cpp
+++ b/src/blackmisc/simulation/aircraftmodel.cpp
@@ -109,7 +109,7 @@ namespace BlackMisc
             meta.forEachMember([ &, this ](auto member)
             {
                 auto &&maybeMemo = helper.maybeMemoize(member.in(*this));
-                json << std::make_pair(CExplicitLatin1String(member.latin1Name()).toJsonKey(), std::cref(maybeMemo));
+                json << std::make_pair(CExplicitLatin1String(member.latin1Name()), std::cref(maybeMemo));
             });
             return json;
         }
diff --git a/src/blackmisc/valuecache.h b/src/blackmisc/valuecache.h
index defff18c4..e26ed572b 100644
--- a/src/blackmisc/valuecache.h
+++ b/src/blackmisc/valuecache.h
@@ -372,7 +372,6 @@ namespace BlackMisc
         }
 
         //! Set a callback to be called when the value is changed by another source.
-        //! \todo Qt 5.7.0: in assert use m_page->parent()->metaObject()->inherits(&U::staticMetaObject)
         template <typename F>
         void setNotifySlot(F slot)
         {
@@ -382,7 +381,7 @@ namespace BlackMisc
                 return;
             }
             using U = typename Private::TClassOfPointerToMember<F>::type;
-            Q_ASSERT_X(m_page->parent()->inherits(U::staticMetaObject.className()), Q_FUNC_INFO, "Slot is member function of wrong class");
+            Q_ASSERT_X(m_page->parent()->metaObject()->inherits(&U::staticMetaObject), Q_FUNC_INFO, "Slot is member function of wrong class");
             m_page->setNotifySlot(*m_element, { [slot](QObject *obj) { Private::invokeSlot(slot, static_cast<U *>(obj)); }, makeId(slot) });
         }