diff --git a/base/PyNucleus_base/blas.pyx b/base/PyNucleus_base/blas.pyx
index 57dde27..d339a2f 100644
--- a/base/PyNucleus_base/blas.pyx
+++ b/base/PyNucleus_base/blas.pyx
@@ -41,7 +41,7 @@ def uninitialized_like(like, **kwargs):
 cpdef carray uninitializedINDEX(tuple shape):
     cdef:
         carray a = carray(shape, 4, 'i')
-        size_t s, i
+        Py_ssize_t s, i
     IF FILL_UNINITIALIZED:
         s = 1
         for i in range(len(shape)):
@@ -54,7 +54,7 @@ cpdef carray uninitializedINDEX(tuple shape):
 cpdef carray uninitializedREAL(tuple shape):
     cdef:
         carray a = carray(shape, 8, 'd')
-        size_t s, i
+        Py_ssize_t s, i
     IF FILL_UNINITIALIZED:
         s = 1
         for i in range(len(shape)):
diff --git a/base/PyNucleus_base/tupleDict.pxd b/base/PyNucleus_base/tupleDict.pxd
index 8287826..4952b31 100644
--- a/base/PyNucleus_base/tupleDict.pxd
+++ b/base/PyNucleus_base/tupleDict.pxd
@@ -72,4 +72,5 @@ cdef class bitArray(indexSet):
 cdef class bitArrayIterator(indexSetIterator):
     cdef:
         bitArray bA
-        INDEX_t k, n
+        INDEX_t k
+        size_t n
diff --git a/base/PyNucleus_base/tupleDict.pyx b/base/PyNucleus_base/tupleDict.pyx
index 5bd2ca4..a10e47c 100644
--- a/base/PyNucleus_base/tupleDict.pyx
+++ b/base/PyNucleus_base/tupleDict.pyx
@@ -451,7 +451,7 @@ cdef class arrayIndexSetIterator(indexSetIterator):
 
 
 cdef class bitArray(indexSet):
-    def __init__(self, INDEX_t hintMaxLength=1, INDEX_t maxElement=0):
+    def __init__(self, size_t hintMaxLength=1, INDEX_t maxElement=0):
         self.length = max(hintMaxLength, maxElement/(sizeof(MEM_t)*8)+1)
         self.a = <MEM_t *>malloc(self.length*sizeof(MEM_t))
         for j in range(self.length):
@@ -562,7 +562,8 @@ cdef class bitArrayIterator(indexSetIterator):
     cdef BOOL_t step(self):
         cdef:
             bitArray bA = self.iS
-            INDEX_t k0, n0, k, n
+            INDEX_t k0, k
+            size_t n0, n
             MEM_t v
 
         if self.n == sizeof(MEM_t)*8-1:
diff --git a/nl/PyNucleus_nl/nonlocalAssembly.pyx b/nl/PyNucleus_nl/nonlocalAssembly.pyx
index e684c8f..7d776d6 100644
--- a/nl/PyNucleus_nl/nonlocalAssembly.pyx
+++ b/nl/PyNucleus_nl/nonlocalAssembly.pyx
@@ -13,6 +13,7 @@ include "config.pxi"
 
 from libc.math cimport sin, cos, M_PI as pi
 from libcpp.map cimport map
+from cpython.long cimport PyLong_FromSsize_t
 from PyNucleus_base.myTypes import INDEX, REAL, COMPLEX, ENCODE, BOOL
 from PyNucleus_base import uninitialized
 from PyNucleus_base.intTuple cimport intTuple
diff --git a/nl/PyNucleus_nl/nonlocalAssembly_{SCALAR}.pxi b/nl/PyNucleus_nl/nonlocalAssembly_{SCALAR}.pxi
index 9fe0389..cc3e030 100644
--- a/nl/PyNucleus_nl/nonlocalAssembly_{SCALAR}.pxi
+++ b/nl/PyNucleus_nl/nonlocalAssembly_{SCALAR}.pxi
@@ -714,7 +714,7 @@ cdef class {SCALAR_label}nonlocalBuilder:
             self.contrib = uninitialized(((2*self.dm.dofs_per_element)*(2*self.dm.dofs_per_element+1)//2), dtype={SCALAR})
         else:
             self.contrib = uninitialized(((2*self.dm.dofs_per_element)**2), dtype={SCALAR})
-        assert self.contrib.shape[0] <= mask.size(), "Mask type size = {} is not large enough for {} entries. Please set a larger size and recompile.".format(mask.size(), self.contrib.shape[0])
+        assert self.contrib.shape[0] <= PyLong_FromSsize_t(mask.size()), "Mask type size = {} is not large enough for {} entries. Please set a larger size and recompile.".format(mask.size(), self.contrib.shape[0])
 
         self.local_matrix.setMesh1(self.dm.mesh)
         if self.dm2 is None: