diff --git a/setup.py b/setup.py
index 81d89b8..3a0f333 100644
--- a/setup.py
+++ b/setup.py
@@ -14,6 +14,7 @@
       install_requires=[
         'numpy>=1.18.1',
         'scipy',
+        'Cython>=0.29.14,<0.30.0',
         'matplotlib'],
       description="Generate STL files from numpy arrays and text",
       author='Tristan Hearn',
diff --git a/stl_tools/cwrapped.c b/stl_tools/cwrapped.c
index ce8c5a2..9c657b5 100644
--- a/stl_tools/cwrapped.c
+++ b/stl_tools/cwrapped.c
@@ -20336,9 +20336,9 @@ static void __pyx_tp_dealloc_array(PyObject *o) {
   {
     PyObject *etype, *eval, *etb;
     PyErr_Fetch(&etype, &eval, &etb);
-    ++Py_REFCNT(o);
+    Py_SET_REFCNT(o, Py_REFCNT(o)+1);
     __pyx_array___dealloc__(o);
-    --Py_REFCNT(o);
+    Py_SET_REFCNT(o, Py_REFCNT(o)-1);
     PyErr_Restore(etype, eval, etb);
   }
   Py_CLEAR(p->mode);
@@ -20647,9 +20647,9 @@ static void __pyx_tp_dealloc_memoryview(PyObject *o) {
   {
     PyObject *etype, *eval, *etb;
     PyErr_Fetch(&etype, &eval, &etb);
-    ++Py_REFCNT(o);
+    Py_SET_REFCNT(o, Py_REFCNT(o)+1);;
     __pyx_memoryview___dealloc__(o);
-    --Py_REFCNT(o);
+    Py_SET_REFCNT(o, Py_REFCNT(o)-1);;
     PyErr_Restore(etype, eval, etb);
   }
   Py_CLEAR(p->obj);
@@ -20897,9 +20897,9 @@ static void __pyx_tp_dealloc__memoryviewslice(PyObject *o) {
   {
     PyObject *etype, *eval, *etb;
     PyErr_Fetch(&etype, &eval, &etb);
-    ++Py_REFCNT(o);
+    Py_SET_REFCNT(o, Py_REFCNT(o)+1);;
     __pyx_memoryviewslice___dealloc__(o);
-    --Py_REFCNT(o);
+    Py_SET_REFCNT(o, Py_REFCNT(o)-1);;
     PyErr_Restore(etype, eval, etb);
   }
   Py_CLEAR(p->from_object);