diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index e7da6630c1f423..9e91d9664ef8a9 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -855,6 +855,19 @@ def test_memory_leak_gh_140939(self):
             b = self.type2test(b'%*b')
             b % (_testcapi.PY_SSIZE_T_MAX, b'abc')
 
+    def test_mod_bytes_lookup_error(self):
+        # An error raised while looking up __bytes__ propagates.
+        class BadBytes:
+            @property
+            def __bytes__(self):
+                raise ZeroDivisionError
+            def __buffer__(self, flags):
+                return memoryview(b'abc')
+
+        b = self.type2test(b'%b')
+        with self.assertRaises(ZeroDivisionError):
+            b % BadBytes()
+
     def test_imod(self):
         b = self.type2test(b'hello, %b!')
         orig = b
diff --git a/Lib/test/test_weakref.py b/Lib/test/test_weakref.py
index d776a311ead2e9..36a0003079c1e9 100644
--- a/Lib/test/test_weakref.py
+++ b/Lib/test/test_weakref.py
@@ -162,6 +162,17 @@ def __getattr__(self, x):
         self.assertIn('MyConfig', repr(obj_weakref))
         self.assertIn('MyConfig', str(obj_weakref))
 
+    def test_repr_name_lookup_error(self):
+        # An error raised while looking up __name__ propagates.
+        class BadName:
+            @property
+            def __name__(self):
+                raise ZeroDivisionError
+
+        obj = BadName()
+        with self.assertRaises(ZeroDivisionError):
+            repr(weakref.ref(obj))
+
     def test_basic_callback(self):
         self.check_basic_callback(C)
         self.check_basic_callback(create_function)
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-10-14-11-40-06.gh-issue-159430.OWpyPm.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-14-11-40-06.gh-issue-159430.OWpyPm.rst
new file mode 100644
index 00000000000000..fb4a6d6da4568a
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-14-11-40-06.gh-issue-159430.OWpyPm.rst
@@ -0,0 +1,2 @@
+Report the correct exception if looking up :meth:`~object.__bytes__` raises
+an exception while performing %-formatting of :class:`bytes`.
diff --git a/Misc/NEWS.d/next/Library/2026-10-14-11-41-00.gh-issue-159430.ZEW-mx.rst b/Misc/NEWS.d/next/Library/2026-10-14-11-41-00.gh-issue-159430.ZEW-mx.rst
new file mode 100644
index 00000000000000..5b9041891431c0
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-10-14-11-41-00.gh-issue-159430.ZEW-mx.rst
@@ -0,0 +1,2 @@
+Report the correct exception if looking up ``__name__`` raises an exception
+when calling :func:`repr` on a :class:`weakref.ref`.
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index 287d1e436fa641..9ee378292cc55e 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -577,6 +577,9 @@ format_obj(PyObject *v, const char **pbuf, Py_ssize_t *plen)
         *plen = PyBytes_GET_SIZE(result);
         return result;
     }
+    else if (PyErr_Occurred()) {
+        return NULL;
+    }
     /* does it support buffer protocol? */
     if (PyObject_CheckBuffer(v)) {
         /* maybe we can avoid making a copy of the buffer object here? */
diff --git a/Objects/weakrefobject.c b/Objects/weakrefobject.c
index d3d5723fbe32e7..6e43861d163096 100644
--- a/Objects/weakrefobject.c
+++ b/Objects/weakrefobject.c
@@ -221,6 +221,10 @@ weakref_repr(PyObject *self)
     }
 
     PyObject *name = _PyObject_LookupSpecial(obj, &_Py_ID(__name__));
+    if (name == NULL && PyErr_Occurred()) {
+        Py_DECREF(obj);
+        return NULL;
+    }
     PyObject *repr;
     if (name == NULL || !PyUnicode_Check(name)) {
         repr = PyUnicode_FromFormat(