2 files changed, 25 insertions, 3 deletions
diff --git a/sources/pyside6/libpyside/pysidesignal.cpp b/sources/pyside6/libpyside/pysidesignal.cpp
index 291de73d8..17071cd1d 100644
--- a/sources/pyside6/libpyside/pysidesignal.cpp
+++ b/sources/pyside6/libpyside/pysidesignal.cpp
@@ -185,7 +185,8 @@ static PyObject *signalInstanceRepr(PyObject *obSelf)
     auto *self = reinterpret_cast<PySideSignalInstance *>(obSelf);
     auto *typeName = Py_TYPE(obSelf)->tp_name;
     return Shiboken::String::fromFormat("<%s %s at %p>", typeName,
-                                        self->d->signature.constData(), obSelf);
+                                        self->d ? self->d->signature.constData()
+                                                : "(no signature)", obSelf);
 }
 
 static PyMethodDef SignalInstance_methods[] = {
@@ -436,6 +437,10 @@ static PyObject *signalInstanceConnect(PyObject *self, PyObject *args, PyObject
         return nullptr;
 
     PySideSignalInstance *source = reinterpret_cast<PySideSignalInstance *>(self);
+    if (!source->d) {
+        PyErr_Format(PyExc_RuntimeError, "cannot connect uninitialized SignalInstance");
+        return nullptr;
+    }
     Shiboken::AutoDecRef pyArgs(PyList_New(0));
 
     bool match = false;
@@ -552,6 +557,10 @@ static int argCountInSignature(const char *signature)
 static PyObject *signalInstanceEmit(PyObject *self, PyObject *args)
 {
     PySideSignalInstance *source = reinterpret_cast<PySideSignalInstance *>(self);
+    if (!source->d) {
+        PyErr_Format(PyExc_RuntimeError, "cannot emit uninitialized SignalInstance");
+        return nullptr;
+    }
 
     // PYSIDE-2201: Check if the object has vanished meanwhile.
     //              Tried to revive it without exception, but this gives problems.
@@ -625,6 +634,10 @@ static PyObject *signalInstanceGetItem(PyObject *self, PyObject *key)
 static PyObject *signalInstanceDisconnect(PyObject *self, PyObject *args)
 {
     auto source = reinterpret_cast<PySideSignalInstance *>(self);
+    if (!source->d) {
+        PyErr_Format(PyExc_RuntimeError, "cannot disconnect uninitialized SignalInstance");
+        return nullptr;
+    }
     Shiboken::AutoDecRef pyArgs(PyList_New(0));
 
     PyObject *slot = Py_None;
diff --git a/sources/pyside6/tests/pysidetest/signalinstance_equality_test.py b/sources/pyside6/tests/pysidetest/signalinstance_equality_test.py
index 732420c4d..d09d63c0e 100644
--- a/sources/pyside6/tests/pysidetest/signalinstance_equality_test.py
+++ b/sources/pyside6/tests/pysidetest/signalinstance_equality_test.py
@@ -12,7 +12,7 @@ init_test_paths(False)
 
 from helper.usesqapplication import UsesQApplication
 
-from PySide6.QtCore import QFile, QObject, QTimer, Signal, Slot
+from PySide6.QtCore import QFile, QObject, QTimer, Signal, SignalInstance, Slot
 from PySide6.QtWidgets import QSlider
 
 
@@ -40,7 +40,16 @@ class TestSignalInstance(unittest.TestCase):
     def test_custom_inherited_signal_instances_are_equal(self):
         o = D()
         self.assertTrue(o.custom_signal == o.custom_signal)
-
+    # additional tests of old errors from 2010 or so
+    def test_uninitialized_SignalInstance(self):
+        # This will no longer crash
+        print(SignalInstance())
+        with self.assertRaises(RuntimeError):
+            SignalInstance().connect(lambda: None)
+        with self.assertRaises(RuntimeError):
+            SignalInstance().disconnect()
+        with self.assertRaises(RuntimeError):
+            SignalInstance().emit()
 
 class MyWidget(QSlider):
     valueChanged = Signal(tuple)