diff --git a/Modules/_pickle.c b/Modules/_pickle.c
--- a/Modules/_pickle.c
+++ b/Modules/_pickle.c
@@ -153,7 +153,7 @@
 static void
 Pdata_dealloc(Pdata *self)
 {
-    int i = Py_SIZE(self);
+    Py_ssize_t i = Py_SIZE(self);
     while (--i >= 0) {
         Py_DECREF(self->data[i]);
     }
@@ -192,7 +192,7 @@
 static int
 Pdata_clear(Pdata *self, int clearto)
 {
-    int i = Py_SIZE(self);
+    Py_ssize_t i = Py_SIZE(self);
 
     if (clearto < 0)
         return stack_underflow();
@@ -369,7 +369,7 @@
     char *errors;               /* Name of errors handling scheme to used when
                                    decoding strings. The default value is
                                    "strict". */
-    int *marks;                 /* Mark stack, used for unpickling container
+    Py_ssize_t *marks;          /* Mark stack, used for unpickling container
                                    objects. */
     Py_ssize_t num_marks;       /* Number of marks in the mark stack. */
     Py_ssize_t marks_size;      /* Current allocated size of the mark stack. */
@@ -700,7 +700,7 @@
     return (result == NULL) ? -1 : 0;
 }
 
-static int
+static Py_ssize_t
 _Pickler_Write(PicklerObject *self, const char *s, Py_ssize_t n)
 {
     Py_ssize_t i, required;
@@ -1267,9 +1267,9 @@
 static int
 memo_put(PicklerObject *self, PyObject *obj)
 {
-    long x;
+    Py_ssize_t x;
     char pdata[30];
-    int len;
+    size_t len;
     int status = 0;
 
     if (self->fast)
@@ -2209,7 +2209,7 @@
 save_list(PicklerObject *self, PyObject *obj)
 {
     char header[3];
-    int len;
+    Py_ssize_t len;
     int status = 0;
 
     if (self->fast && !fast_save_enter(self, obj))
@@ -2469,7 +2469,7 @@
 {
     PyObject *items, *iter;
     char header[3];
-    int len;
+    Py_ssize_t len;
     int status = 0;
 
     if (self->fast && !fast_save_enter(self, obj))
@@ -3795,7 +3795,7 @@
                                module_name, global_name);
 }
 
-static int
+static Py_ssize_t
 marker(UnpicklerObject *self)
 {
     if (self->num_marks < 1) {
@@ -4343,7 +4343,7 @@
 load_dict(UnpicklerObject *self)
 {
     PyObject *dict, *key, *value;
-    int i, j, k;
+    Py_ssize_t i, j, k;
 
     if ((i = marker(self)) < 0)
         return -1;
@@ -4612,7 +4612,7 @@
 static int
 load_pop(UnpicklerObject *self)
 {
-    int len = Py_SIZE(self->stack);
+    Py_ssize_t len = Py_SIZE(self->stack);
 
     /* Note that we split the (pickle.py) stack into two stacks,
      * an object stack and a mark stack. We have to be clever and
@@ -4650,7 +4650,7 @@
 load_dup(UnpicklerObject *self)
 {
     PyObject *last;
-    int len;
+    Py_ssize_t len;
 
     if ((len = Py_SIZE(self->stack)) <= 0)
         return stack_underflow();
@@ -4887,11 +4887,11 @@
 }
 
 static int
-do_append(UnpicklerObject *self, int x)
+do_append(UnpicklerObject *self, Py_ssize_t x)
 {
     PyObject *value;
     PyObject *list;
-    int len, i;
+    Py_ssize_t len, i;
 
     len = Py_SIZE(self->stack);
     if (x > len || x <= 0)
@@ -4954,7 +4954,7 @@
 {
     PyObject *value, *key;
     PyObject *dict;
-    int len, i;
+    Py_ssize_t len, i;
     int status = 0;
 
     len = Py_SIZE(self->stack);
@@ -5122,7 +5122,7 @@
 
     if ((self->num_marks + 1) >= self->marks_size) {
         size_t alloc;
-        int *marks;
+        Py_ssize_t *marks;
 
         /* Use the size_t type to check for overflow. */
         alloc = ((size_t)self->num_marks << 1) + 20;
@@ -5133,9 +5133,9 @@
         }
 
         if (self->marks == NULL)
-            marks = (int *)PyMem_Malloc(alloc * sizeof(int));
+            marks = PyMem_Malloc(alloc * sizeof(int));
         else
-            marks = (int *)PyMem_Realloc(self->marks, alloc * sizeof(int));
+            marks = PyMem_Realloc(self->marks, alloc * sizeof(int));
         if (marks == NULL) {
             PyErr_NoMemory();
             return -1;