diff --git a/pyproject.toml b/pyproject.toml
index 81f300d..665c223 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [build-system]
 requires = [
     "setuptools",
-    "cython>=0.29.1,<0.30.0",
+    "cython>=0.29.1",
 ]
 build-backend = "setuptools.build_meta"
diff --git a/requirements.txt b/requirements.txt
index 33a1960..0701d8e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 catalogue>=2.0.3,<2.1.0
 # Development requirements
-cython>=0.29.1,<0.30.0
+cython>=0.29.1
 pytest>=4.6.5
 pytest-timeout>=1.3.3,<2.0.0
 mock>=2.0.0,<3.0.0
diff --git a/setup.cfg b/setup.cfg
index d595699..f00db42 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -30,7 +30,7 @@ zip_safe = true
 include_package_data = true
 python_requires = >=3.6
 setup_requires =
-    cython>=0.29.1,<0.30.0
+    cython>=0.29.1
 install_requires =
     catalogue>=2.0.3,<2.1.0
 
diff --git a/srsly/msgpack/_unpacker.pyx b/srsly/msgpack/_unpacker.pyx
index b6c5f04..fb1bd93 100644
--- a/srsly/msgpack/_unpacker.pyx
+++ b/srsly/msgpack/_unpacker.pyx
@@ -10,7 +10,7 @@ cdef extern from "Python.h":
 from libc.stdlib cimport *
 from libc.string cimport *
 from libc.limits cimport *
-ctypedef unsigned long long uint64_t
+from libc.stdint cimport uint64_t
 
 from .exceptions import (
     BufferFull,