diff --git a/py/obj.h b/py/obj.h
index 03dadeb07e..93078b81e1 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -819,17 +819,17 @@ typedef struct {
     mp_int_t step;
 } mp_bound_slice_t;
 
-void mp_seq_multiply(const void *items, mp_uint_t item_sz, mp_uint_t len, mp_uint_t times, void *dest);
+void mp_seq_multiply(const void *items, size_t item_sz, size_t len, size_t times, void *dest);
 #if MICROPY_PY_BUILTINS_SLICE
 bool mp_seq_get_fast_slice_indexes(mp_uint_t len, mp_obj_t slice, mp_bound_slice_t *indexes);
 #endif
 #define mp_seq_copy(dest, src, len, item_t) memcpy(dest, src, len * sizeof(item_t))
 #define mp_seq_cat(dest, src1, len1, src2, len2, item_t) { memcpy(dest, src1, (len1) * sizeof(item_t)); memcpy(dest + (len1), src2, (len2) * sizeof(item_t)); }
-bool mp_seq_cmp_bytes(mp_uint_t op, const byte *data1, mp_uint_t len1, const byte *data2, mp_uint_t len2);
-bool mp_seq_cmp_objs(mp_uint_t op, const mp_obj_t *items1, mp_uint_t len1, const mp_obj_t *items2, mp_uint_t len2);
-mp_obj_t mp_seq_index_obj(const mp_obj_t *items, mp_uint_t len, mp_uint_t n_args, const mp_obj_t *args);
-mp_obj_t mp_seq_count_obj(const mp_obj_t *items, mp_uint_t len, mp_obj_t value);
-mp_obj_t mp_seq_extract_slice(mp_uint_t len, const mp_obj_t *seq, mp_bound_slice_t *indexes);
+bool mp_seq_cmp_bytes(mp_uint_t op, const byte *data1, size_t len1, const byte *data2, size_t len2);
+bool mp_seq_cmp_objs(mp_uint_t op, const mp_obj_t *items1, size_t len1, const mp_obj_t *items2, size_t len2);
+mp_obj_t mp_seq_index_obj(const mp_obj_t *items, size_t len, size_t n_args, const mp_obj_t *args);
+mp_obj_t mp_seq_count_obj(const mp_obj_t *items, size_t len, mp_obj_t value);
+mp_obj_t mp_seq_extract_slice(size_t len, const mp_obj_t *seq, mp_bound_slice_t *indexes);
 // Helper to clear stale pointers from allocated, but unused memory, to preclude GC problems
 #define mp_seq_clear(start, len, alloc_len, item_sz) memset((byte*)(start) + (len) * (item_sz), 0, ((alloc_len) - (len)) * (item_sz))
 #define mp_seq_replace_slice_no_grow(dest, dest_len, beg, end, slice, slice_len, item_sz) \
diff --git a/py/sequence.c b/py/sequence.c
index 9aa3b6a896..11761f6518 100644
--- a/py/sequence.c
+++ b/py/sequence.c
@@ -38,9 +38,9 @@
 
 // Implements backend of sequence * integer operation. Assumes elements are
 // memory-adjacent in sequence.
-void mp_seq_multiply(const void *items, mp_uint_t item_sz, mp_uint_t len, mp_uint_t times, void *dest) {
-    for (mp_uint_t i = 0; i < times; i++) {
-        uint copy_sz = item_sz * len;
+void mp_seq_multiply(const void *items, size_t item_sz, size_t len, size_t times, void *dest) {
+    for (size_t i = 0; i < times; i++) {
+        size_t copy_sz = item_sz * len;
         memcpy(dest, items, copy_sz);
         dest = (char*)dest + copy_sz;
     }
@@ -119,7 +119,7 @@ bool mp_seq_get_fast_slice_indexes(mp_uint_t len, mp_obj_t slice, mp_bound_slice
 
 #endif
 
-mp_obj_t mp_seq_extract_slice(mp_uint_t len, const mp_obj_t *seq, mp_bound_slice_t *indexes) {
+mp_obj_t mp_seq_extract_slice(size_t len, const mp_obj_t *seq, mp_bound_slice_t *indexes) {
     (void)len; // TODO can we remove len from the arg list?
 
     mp_int_t start = indexes->start, stop = indexes->stop;
@@ -143,7 +143,7 @@ mp_obj_t mp_seq_extract_slice(mp_uint_t len, const mp_obj_t *seq, mp_bound_slice
 
 // Special-case comparison function for sequences of bytes
 // Don't pass MP_BINARY_OP_NOT_EQUAL here
-bool mp_seq_cmp_bytes(mp_uint_t op, const byte *data1, mp_uint_t len1, const byte *data2, mp_uint_t len2) {
+bool mp_seq_cmp_bytes(mp_uint_t op, const byte *data1, size_t len1, const byte *data2, size_t len2) {
     if (op == MP_BINARY_OP_EQUAL && len1 != len2) {
         return false;
     }
@@ -151,14 +151,14 @@ bool mp_seq_cmp_bytes(mp_uint_t op, const byte *data1, mp_uint_t len1, const byt
     // Let's deal only with > & >=
     if (op == MP_BINARY_OP_LESS || op == MP_BINARY_OP_LESS_EQUAL) {
         SWAP(const byte*, data1, data2);
-        SWAP(uint, len1, len2);
+        SWAP(size_t, len1, len2);
         if (op == MP_BINARY_OP_LESS) {
             op = MP_BINARY_OP_MORE;
         } else {
             op = MP_BINARY_OP_MORE_EQUAL;
         }
     }
-    uint min_len = len1 < len2 ? len1 : len2;
+    size_t min_len = len1 < len2 ? len1 : len2;
     int res = memcmp(data1, data2, min_len);
     if (op == MP_BINARY_OP_EQUAL) {
         // If we are checking for equality, here're the answer
@@ -187,7 +187,7 @@ bool mp_seq_cmp_bytes(mp_uint_t op, const byte *data1, mp_uint_t len1, const byt
 
 // Special-case comparison function for sequences of mp_obj_t
 // Don't pass MP_BINARY_OP_NOT_EQUAL here
-bool mp_seq_cmp_objs(mp_uint_t op, const mp_obj_t *items1, mp_uint_t len1, const mp_obj_t *items2, mp_uint_t len2) {
+bool mp_seq_cmp_objs(mp_uint_t op, const mp_obj_t *items1, size_t len1, const mp_obj_t *items2, size_t len2) {
     if (op == MP_BINARY_OP_EQUAL && len1 != len2) {
         return false;
     }
@@ -195,7 +195,7 @@ bool mp_seq_cmp_objs(mp_uint_t op, const mp_obj_t *items1, mp_uint_t len1, const
     // Let's deal only with > & >=
     if (op == MP_BINARY_OP_LESS || op == MP_BINARY_OP_LESS_EQUAL) {
         SWAP(const mp_obj_t *, items1, items2);
-        SWAP(uint, len1, len2);
+        SWAP(size_t, len1, len2);
         if (op == MP_BINARY_OP_LESS) {
             op = MP_BINARY_OP_MORE;
         } else {
@@ -203,8 +203,8 @@ bool mp_seq_cmp_objs(mp_uint_t op, const mp_obj_t *items1, mp_uint_t len1, const
         }
     }
 
-    mp_uint_t len = len1 < len2 ? len1 : len2;
-    for (mp_uint_t i = 0; i < len; i++) {
+    size_t len = len1 < len2 ? len1 : len2;
+    for (size_t i = 0; i < len; i++) {
         // If current elements equal, can't decide anything - go on
         if (mp_obj_equal(items1[i], items2[i])) {
             continue;
@@ -236,7 +236,7 @@ bool mp_seq_cmp_objs(mp_uint_t op, const mp_obj_t *items1, mp_uint_t len1, const
 }
 
 // Special-case of index() which searches for mp_obj_t
-mp_obj_t mp_seq_index_obj(const mp_obj_t *items, mp_uint_t len, mp_uint_t n_args, const mp_obj_t *args) {
+mp_obj_t mp_seq_index_obj(const mp_obj_t *items, size_t len, size_t n_args, const mp_obj_t *args) {
     mp_obj_type_t *type = mp_obj_get_type(args[0]);
     mp_obj_t value = args[1];
     size_t start = 0;
@@ -259,9 +259,9 @@ mp_obj_t mp_seq_index_obj(const mp_obj_t *items, mp_uint_t len, mp_uint_t n_args
     mp_raise_msg(&mp_type_ValueError, "object not in sequence");
 }
 
-mp_obj_t mp_seq_count_obj(const mp_obj_t *items, mp_uint_t len, mp_obj_t value) {
-    mp_uint_t count = 0;
-    for (uint i = 0; i < len; i++) {
+mp_obj_t mp_seq_count_obj(const mp_obj_t *items, size_t len, mp_obj_t value) {
+    size_t count = 0;
+    for (size_t i = 0; i < len; i++) {
          if (mp_obj_equal(items[i], value)) {
               count++;
          }