--- src/block_template.c
+++ src/block_template.c
@@ -33,6 +33,7 @@
 #include <string.h>
 #endif
 
+#define PY_SSIZE_T_CLEAN
 #include "Python.h"
 #include "pycrypto_compat.h"
 #include "modsupport.h" 
@@ -123,7 +124,8 @@ ALGnew(PyObject *self, PyObject *args, P
 {
 	unsigned char *key, *IV;
 	ALGobject * new=NULL;
-	int keylen, IVlen=0, mode=MODE_ECB, segment_size=0;
+	Py_ssize_t keylen, IVlen=0;
+	int mode=MODE_ECB, segment_size=0;
 	PyObject *counter = NULL;
 	int counter_shortcut = 0;
 #ifdef PCT_ARC2_MODULE
@@ -161,7 +163,7 @@ ALGnew(PyObject *self, PyObject *args, P
 	{
 		PyErr_Format(PyExc_ValueError,
 			     "Key must be %i bytes long, not %i",
-			     KEY_SIZE, keylen);
+			     KEY_SIZE, (int)keylen);
 		return NULL;
 	}
 	if (KEY_SIZE==0 && keylen==0)
@@ -242,7 +244,7 @@ ALGnew(PyObject *self, PyObject *args, P
         new->st.effective_keylen = effective_keylen;
 #endif
 
-	block_init(&(new->st), key, keylen);
+	block_init(&(new->st), key, (int)keylen);
 	if (PyErr_Occurred())
 	{
 		Py_DECREF(new);
@@ -250,7 +252,7 @@ ALGnew(PyObject *self, PyObject *args, P
 	}
 	memset(new->IV, 0, BLOCK_SIZE);
 	memset(new->oldCipher, 0, BLOCK_SIZE);
-	memcpy(new->IV, IV, IVlen);
+	memcpy(new->IV, IV, (size_t)IVlen);
 	new->mode = mode;
 	new->count=BLOCK_SIZE;   /* stores how many bytes in new->oldCipher have been used */
 	return new;
@@ -265,10 +267,12 @@ ALG_Encrypt(ALGobject *self, PyObject *a
 	unsigned char *buffer, *str;
 	unsigned char temp[BLOCK_SIZE];
 	int i, j, len;
+	Py_ssize_t param_len;
 	PyObject *result;
   
-	if (!PyArg_Parse(args, "s#", &str, &len))
+	if (!PyArg_Parse(args, "s#", &str, &param_len))
 		return NULL;
+	len = (int)param_len;
 	if (len==0)			/* Handle empty string */
 	{
 		return PyBytes_FromStringAndSize(NULL, 0);
@@ -497,14 +501,16 @@ ALG_Decrypt(ALGobject *self, PyObject *a
 	unsigned char *buffer, *str;
 	unsigned char temp[BLOCK_SIZE];
 	int i, j, len;
+	Py_ssize_t param_len;
 	PyObject *result;
 
 	/* CTR mode decryption is identical to encryption */
 	if (self->mode == MODE_CTR)
 		return ALG_Encrypt(self, args);
 
-	if (!PyArg_Parse(args, "s#", &str, &len))
+	if (!PyArg_Parse(args, "s#", &str, &param_len))
 		return NULL;
+	len = (int)param_len;
 	if (len==0)			/* Handle empty string */
 	{
 		return PyBytes_FromStringAndSize(NULL, 0);
--- src/hash_template.c
+++ src/hash_template.c
@@ -30,6 +30,7 @@
 #ifdef _HAVE_STDC_HEADERS
 #include <string.h>
 #endif
+#define PY_SSIZE_T_CLEAN
 #include "Python.h"
 #include "pycrypto_compat.h"
 
@@ -163,7 +164,7 @@ static PyObject *
 ALG_update(ALGobject *self, PyObject *args)
 {
 	unsigned char *cp;
-	int len;
+	Py_ssize_t len;
 
 	if (!PyArg_ParseTuple(args, "s#", &cp, &len))
 		return NULL;
@@ -273,7 +274,7 @@ ALG_new(PyObject *self, PyObject *args)
 {
         ALGobject *new;
 	unsigned char *cp = NULL;
-	int len;
+	Py_ssize_t len;
 	
 	if ((new = newALGobject()) == NULL)
 		return NULL;
--- src/stream_template.c
+++ src/stream_template.c
@@ -33,6 +33,7 @@
 #include <string.h>
 #endif
 
+#define PY_SSIZE_T_CLEAN
 #include "Python.h"
 #include "pycrypto_compat.h"
 #include "modsupport.h"
@@ -100,7 +101,7 @@ ALGnew(PyObject *self, PyObject *args, P
 {
 	unsigned char *key;
 	ALGobject * new;
-	int keylen;
+	Py_ssize_t keylen;
 
 	new = newALGobject();
 	if (!PyArg_ParseTupleAndKeywords(args, kwdict, "s#", kwlist, 
@@ -124,7 +125,7 @@ ALGnew(PyObject *self, PyObject *args, P
 				"the null string (0 bytes long)");
 		return NULL;
 	}
-	stream_init(&(new->st), key, keylen);
+	stream_init(&(new->st), key, (int)keylen);
 	if (PyErr_Occurred())
 	{
 		Py_DECREF(new);
@@ -141,10 +142,12 @@ ALG_Encrypt(ALGobject *self, PyObject *a
 {
 	unsigned char *buffer, *str;
 	int len;
+	Py_ssize_t param_len;
 	PyObject *result;
 
-	if (!PyArg_Parse(args, "s#", &str, &len))
+	if (!PyArg_Parse(args, "s#", &str, &param_len))
 		return NULL;
+	len = (int)param_len;
 	if (len == 0)			/* Handle empty string */
 	{
 		return PyBytes_FromStringAndSize(NULL, 0);
@@ -173,10 +176,12 @@ ALG_Decrypt(ALGobject *self, PyObject *a
 {
 	unsigned char *buffer, *str;
 	int len;
+	Py_ssize_t param_len;
 	PyObject *result;
 
-	if (!PyArg_Parse(args, "s#", &str, &len))
+	if (!PyArg_Parse(args, "s#", &str, &param_len))
 		return NULL;
+	len = (int)param_len;
 	if (len == 0)			/* Handle empty string */
 	{
 		return PyBytes_FromStringAndSize(NULL, 0);