diff -up PyQt4_gpl_x11-4.12.3/qpy/QtCore/qpycore_classinfo.cpp.me PyQt4_gpl_x11-4.12.3/qpy/QtCore/qpycore_classinfo.cpp
--- PyQt4_gpl_x11-4.12.3/qpy/QtCore/qpycore_classinfo.cpp.me	2022-06-21 15:04:28.885197054 +0200
+++ PyQt4_gpl_x11-4.12.3/qpy/QtCore/qpycore_classinfo.cpp	2022-06-21 15:04:51.654741730 +0200
@@ -36,7 +36,7 @@ PyObject *qpycore_ClassInfo(const char *
 
     // We need the frame we were called from, not the current one.
     if (frame)
-        frame = frame->f_back;
+        frame = PyFrame_GetBack(frame);
 
     if (!frame)
     {