diff --git a/newsfragments/5946.changed.md b/newsfragments/5946.changed.md
new file mode 100644
index 00000000000..5e606663272
--- /dev/null
+++ b/newsfragments/5946.changed.md
@@ -0,0 +1,3 @@
+Removed use of the CPython-internal `_PyUnicode_COMPACT_DATA` symbol from PyO3's FFI test suite.
+Removed `_PySet_NextEntry` in `pyo3-ffi`; it is a CPython-internal API with no stability guarantee.
+Removed `_PyLong_NumBits` in `pyo3-ffi` and replaced its internal use with `int.bit_length()` for Python < 3.13 builds.
diff --git a/pyo3-ffi/src/impl_/macros.rs b/pyo3-ffi/src/impl_/macros.rs
index c493157186c..c5ca00a029e 100644
--- a/pyo3-ffi/src/impl_/macros.rs
+++ b/pyo3-ffi/src/impl_/macros.rs
@@ -248,12 +248,6 @@ macro_rules! extern_libpython_maybe_private_fn {
     ) => {
         extern_libpython_cpython_private_fn! { $(#[$attrs])* $vis $name($($args)*) $(-> $ret)? }
     };
-    (
-        [_PySet_NextEntry]
-        $(#[$attrs:meta])* $vis:vis fn $name:ident($($args:tt)*) $(-> $ret:ty)?
-    ) => {
-        extern_libpython_cpython_private_fn! { $(#[$attrs])* $vis $name($($args)*) $(-> $ret)? }
-    };
     (
         [$name:ident]
         $(#[$attrs:meta])* $vis:vis fn $fn_name:ident($($args:tt)*) $(-> $ret:ty)?
diff --git a/pyo3-ffi/src/longobject.rs b/pyo3-ffi/src/longobject.rs
index 7aab545777e..4ecd22ce8fc 100644
--- a/pyo3-ffi/src/longobject.rs
+++ b/pyo3-ffi/src/longobject.rs
@@ -85,6 +85,8 @@ extern_libpython! {
 #[cfg(not(Py_LIMITED_API))]
 extern_libpython! {
     #[cfg_attr(PyPy, link_name = "_PyPyLong_NumBits")]
+    #[cfg(not(Py_3_13))]
+    #[doc(hidden)]
     pub fn _PyLong_NumBits(obj: *mut PyObject) -> size_t;
 }
 
diff --git a/pyo3-ffi/src/setobject.rs b/pyo3-ffi/src/setobject.rs
index b56ed5d1cd5..8a22415257f 100644
--- a/pyo3-ffi/src/setobject.rs
+++ b/pyo3-ffi/src/setobject.rs
@@ -41,15 +41,7 @@ pub unsafe fn PySet_GET_SIZE(so: *mut PyObject) -> Py_ssize_t {
 // skipped _PySet_Dummy
 
 extern_libpython! {
-    #[cfg(not(Py_LIMITED_API))]
-    #[cfg_attr(PyPy, link_name = "_PyPySet_NextEntry")]
-    pub fn _PySet_NextEntry(
-        set: *mut PyObject,
-        pos: *mut Py_ssize_t,
-        key: *mut *mut PyObject,
-        hash: *mut super::Py_hash_t,
-    ) -> c_int;
-
+    // skipped non-limited _PySet_NextEntry
     // skipped non-limited _PySet_Update
 }
 
diff --git a/src/conversions/num_bigint.rs b/src/conversions/num_bigint.rs
index cdc77d8b095..c11ca92e6a5 100644
--- a/src/conversions/num_bigint.rs
+++ b/src/conversions/num_bigint.rs
@@ -318,24 +318,9 @@ fn int_to_py_bytes<'py>(
 #[inline]
 #[cfg(any(not(Py_3_13), Py_LIMITED_API))]
 fn int_n_bits(long: &Bound<'_, PyInt>) -> PyResult<usize> {
-    let py = long.py();
-    #[cfg(not(Py_LIMITED_API))]
-    {
-        // fast path
-        let n_bits = unsafe { crate::ffi::_PyLong_NumBits(long.as_ptr()) };
-        if n_bits == (-1isize as usize) {
-            return Err(crate::PyErr::fetch(py));
-        }
-        Ok(n_bits)
-    }
-
-    #[cfg(Py_LIMITED_API)]
-    {
-        // slow path
-        use crate::types::PyAnyMethods;
-        long.call_method0(crate::intern!(py, "bit_length"))
-            .and_then(|any| any.extract())
-    }
+    use crate::types::PyAnyMethods;
+    long.call_method0(crate::intern!(long.py(), "bit_length"))
+        .and_then(|any| any.extract())
 }
 
 #[cfg(test)]
diff --git a/src/ffi/tests.rs b/src/ffi/tests.rs
index 8b5226dd444..203669083c0 100644
--- a/src/ffi/tests.rs
+++ b/src/ffi/tests.rs
@@ -200,8 +200,6 @@ fn ascii() {
             // 2 and 4 byte macros return nonsense for this string instance.
             assert_eq!(PyUnicode_KIND(ptr), PyUnicode_1BYTE_KIND);
 
-            #[cfg(not(Py_3_14))]
-            assert!(!_PyUnicode_COMPACT_DATA(ptr).is_null());
             // _PyUnicode_NONCOMPACT_DATA isn't valid for compact strings.
             assert!(!PyUnicode_DATA(ptr).is_null());
 
@@ -243,8 +241,6 @@ fn ucs4() {
             assert!(!PyUnicode_4BYTE_DATA(ptr).is_null());
             assert_eq!(PyUnicode_KIND(ptr), PyUnicode_4BYTE_KIND);
 
-            #[cfg(not(Py_3_14))]
-            assert!(!_PyUnicode_COMPACT_DATA(ptr).is_null());
             // _PyUnicode_NONCOMPACT_DATA isn't valid for compact strings.
             assert!(!PyUnicode_DATA(ptr).is_null());