diff --git a/src/dbus/qdbusextratypes.cpp b/src/dbus/qdbusextratypes.cpp
index 355a764e9cd..1f976939668 100644
--- a/src/dbus/qdbusextratypes.cpp
+++ b/src/dbus/qdbusextratypes.cpp
@@ -34,6 +34,10 @@ void QDBusObjectPath::doCheck()
     }
 }
 
+QDBusSignature::QDBusSignature() noexcept
+    : m_signature(QLatin1StringView("")) // mark non-null (empty signatures are valid)
+{}
+
 void QDBusSignature::doCheck()
 {
     if (!QDBusUtil::isValidSignature(m_signature)) {
diff --git a/src/dbus/qdbusextratypes.h b/src/dbus/qdbusextratypes.h
index cb63df4f932..3b44bfc2175 100644
--- a/src/dbus/qdbusextratypes.h
+++ b/src/dbus/qdbusextratypes.h
@@ -77,9 +77,7 @@ class Q_DBUS_EXPORT QDBusSignature
 {
     QString m_signature;
 public:
-    QDBusSignature() noexcept
-        : m_signature(QLatin1StringView("")) // mark non-null (empty signatures are valid)
-    {}
+    QDBusSignature() noexcept;
     // compiler-generated copy/move constructor/assignment operators are ok!
     // compiler-generated destructor is ok!