diff --git a/av/sidedata/motionvectors.py b/av/sidedata/motionvectors.py
index 04e06f25e..dcf0e9913 100644
--- a/av/sidedata/motionvectors.py
+++ b/av/sidedata/motionvectors.py
@@ -1,6 +1,7 @@
 import cython
 from cython.cimports import libav as lib
 from cython.cimports.av.sidedata.sidedata import SideData
+from cython.cimports.libc.stdint import uintptr_t
 
 _cinit_bypass_sentinel = cython.declare(object, object())
 
@@ -15,7 +16,7 @@ def __init__(self, sentinel, frame: Frame, index: cython.int):
     def __repr__(self):
         return (
             f"<av.sidedata.MotionVectors {self.ptr.size} bytes "
-            f"of {len(self)} vectors at 0x{cython.cast(cython.uint, self.ptr.data):0x}>"
+            f"of {len(self)} vectors at 0x{cython.cast(uintptr_t, self.ptr.data):0x}>"
         )
 
     def __len__(self):
diff --git a/av/sidedata/sidedata.py b/av/sidedata/sidedata.py
index 24f58a3e0..f19aeac06 100644
--- a/av/sidedata/sidedata.py
+++ b/av/sidedata/sidedata.py
@@ -2,7 +2,7 @@
 from enum import Enum
 
 import cython
-from cython.cimports.libc.stdint import int32_t
+from cython.cimports.libc.stdint import int32_t, uintptr_t
 
 from av.sidedata.encparams import VideoEncParams
 from av.sidedata.motionvectors import MotionVectors
@@ -95,7 +95,7 @@ def _buffer_writable(self) -> cython.bint:
         return False
 
     def __repr__(self):
-        return f"<av.sidedata.{self.__class__.__name__} {self.ptr.size} bytes of {self.type} at 0x{cython.cast(cython.uint, self.ptr.data):0x}>"
+        return f"<av.sidedata.{self.__class__.__name__} {self.ptr.size} bytes of {self.type} at 0x{cython.cast(uintptr_t, self.ptr.data):0x}>"
 
     @property
     def type(self):