diff --git a/py/objset.c b/py/objset.c
index 9a7e6751f5..448f484d5a 100644
--- a/py/objset.c
+++ b/py/objset.c
@@ -128,7 +128,7 @@ STATIC mp_obj_t set_copy(mp_obj_t self_in) {
 
     mp_obj_set_t *other = m_new_obj(mp_obj_set_t);
     other->base.type = &mp_type_set;
-    mp_set_init(&other->set, self->set.alloc - 1);
+    mp_set_init(&other->set, self->set.alloc);
     other->set.used = self->set.used;
     memcpy(other->set.table, self->set.table, self->set.alloc * sizeof(mp_obj_t));
 
diff --git a/py/objstr.c b/py/objstr.c
index 329dfe6dd9..4395757a46 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -1106,22 +1106,31 @@ STATIC mp_obj_t str_modulo_format(mp_obj_t pattern, uint n_args, const mp_obj_t
 
 STATIC mp_obj_t str_replace(uint n_args, const mp_obj_t *args) {
     assert(MP_OBJ_IS_STR(args[0]));
-    assert(MP_OBJ_IS_STR(args[1]));
-    assert(MP_OBJ_IS_STR(args[2]));
 
-    machine_int_t max_rep = 0;
+    machine_int_t max_rep = -1;
     if (n_args == 4) {
-        assert(MP_OBJ_IS_SMALL_INT(args[3]));
-        max_rep = MP_OBJ_SMALL_INT_VALUE(args[3]);
+        max_rep = mp_obj_get_int(args[3]);
         if (max_rep == 0) {
             return args[0];
         } else if (max_rep < 0) {
-            max_rep = 0;
+            max_rep = -1;
         }
     }
 
     // if max_rep is still 0 by this point we will need to do all possible replacements
 
+    // check argument types
+
+    if (!MP_OBJ_IS_STR(args[1])) {
+        bad_implicit_conversion(args[1]);
+    }
+
+    if (!MP_OBJ_IS_STR(args[2])) {
+        bad_implicit_conversion(args[2]);
+    }
+
+    // extract string data
+
     GET_STR_DATA_LEN(args[0], str, str_len);
     GET_STR_DATA_LEN(args[1], old, old_len);
     GET_STR_DATA_LEN(args[2], new, new_len);
@@ -1143,8 +1152,20 @@ STATIC mp_obj_t str_replace(uint n_args, const mp_obj_t *args) {
         machine_uint_t num_replacements_done = 0;
         const byte *old_occurrence;
         const byte *offset_ptr = str;
-        machine_uint_t offset_num = 0;
-        while ((old_occurrence = find_subbytes(offset_ptr, str_len - offset_num, old, old_len, 1)) != NULL) {
+        machine_uint_t str_len_remain = str_len;
+        if (old_len == 0) {
+            // if old_str is empty, copy new_str to start of replaced string
+            // copy the replacement string
+            if (data != NULL) {
+                memcpy(data, new, new_len);
+            }
+            replaced_str_index += new_len;
+            num_replacements_done++;
+        }
+        while (num_replacements_done != max_rep && str_len_remain > 0 && (old_occurrence = find_subbytes(offset_ptr, str_len_remain, old, old_len, 1)) != NULL) {
+            if (old_len == 0) {
+                old_occurrence += 1;
+            }
             // copy from just after end of last occurrence of to-be-replaced string to right before start of next occurrence
             if (data != NULL) {
                 memcpy(data + replaced_str_index, offset_ptr, old_occurrence - offset_ptr);
@@ -1156,19 +1177,15 @@ STATIC mp_obj_t str_replace(uint n_args, const mp_obj_t *args) {
             }
             replaced_str_index += new_len;
             offset_ptr = old_occurrence + old_len;
-            offset_num = offset_ptr - str;
-
+            str_len_remain = str + str_len - offset_ptr;
             num_replacements_done++;
-            if (max_rep != 0 && num_replacements_done == max_rep){
-                break;
-            }
         }
 
         // copy from just after end of last occurrence of to-be-replaced string to end of old string
         if (data != NULL) {
-            memcpy(data + replaced_str_index, offset_ptr, str_len - offset_num);
+            memcpy(data + replaced_str_index, offset_ptr, str_len_remain);
         }
-        replaced_str_index += str_len - offset_num;
+        replaced_str_index += str_len_remain;
 
         if (data == NULL) {
             // first pass
@@ -1178,6 +1195,7 @@ STATIC mp_obj_t str_replace(uint n_args, const mp_obj_t *args) {
             } else {
                 // substr found, allocate new string
                 replaced_str = mp_obj_str_builder_start(mp_obj_get_type(args[0]), replaced_str_index, &data);
+                assert(data != NULL);
             }
         } else {
             // second pass, we are done
diff --git a/tests/basics/iter-of-iter.py b/tests/basics/iter-of-iter.py
index ba55356294..70282aa97e 100644
--- a/tests/basics/iter-of-iter.py
+++ b/tests/basics/iter-of-iter.py
@@ -5,4 +5,4 @@ print(list(i))
 i = iter(iter({1:2, 3:4, 5:6}))
 print(sorted(i))
 i = iter(iter({1, 2, 3}))
-print(list(i))
+print(sorted(i))
diff --git a/tests/basics/set1.py b/tests/basics/set1.py
index c54fbd8379..399c33eb68 100644
--- a/tests/basics/set1.py
+++ b/tests/basics/set1.py
@@ -4,4 +4,4 @@ s = {1}
 print(s)
 
 s = {3, 4, 3, 1}
-print(s)
+print(sorted(s))
diff --git a/tests/basics/set_binop.py b/tests/basics/set_binop.py
index d0d0b8027b..1acb810f0f 100644
--- a/tests/basics/set_binop.py
+++ b/tests/basics/set_binop.py
@@ -5,26 +5,26 @@ def r(s):
 sets = [set(), {1}, {1, 2}, {1, 2, 3}, {2, 3}, {2, 3, 5}, {5}, {7}]
 for s in sets:
     for t in sets:
-        print(s, '|', t, '=', r(s | t))
-        print(s, '^', t, '=', r(s ^ t))
-        print(s, '&', t, '=', r(s & t))
-        print(s, '-', t, '=', r(s - t))
+        print(r(s), '|', r(t), '=', r(s | t))
+        print(r(s), '^', r(t), '=', r(s ^ t))
+        print(r(s), '&', r(t), '=', r(s & t))
+        print(r(s), '-', r(t), '=', r(s - t))
         u = s.copy()
         u |= t
-        print(s, "|=", t, '-->', r(u))
+        print(r(s), "|=", r(t), '-->', r(u))
         u = s.copy()
         u ^= t
-        print(s, "^=", t, '-->', r(u))
+        print(r(s), "^=", r(t), '-->', r(u))
         u = s.copy()
         u &= t
-        print(s, "&=", t, "-->", r(u))
+        print(r(s), "&=", r(t), "-->", r(u))
         u = s.copy()
         u -= t
-        print(s, "-=", t, "-->", r(u))
+        print(r(s), "-=", r(t), "-->", r(u))
 
-        print(s, '==', t, '=', s == t)
-        print(s, '!=', t, '=', s != t)
-        print(s, '>', t, '=', s > t)
-        print(s, '>=', t, '=', s >= t)
-        print(s, '<', t, '=', s < t)
-        print(s, '<=', t, '=', s <= t)
+        print(r(s), '==', r(t), '=', s == t)
+        print(r(s), '!=', r(t), '=', s != t)
+        print(r(s), '>', r(t), '=', s > t)
+        print(r(s), '>=', r(t), '=', s >= t)
+        print(r(s), '<', r(t), '=', s < t)
+        print(r(s), '<=', r(t), '=', s <= t)
diff --git a/tests/basics/set_symmetric_difference.py b/tests/basics/set_symmetric_difference.py
index acf298385a..d5f1df1ed7 100644
--- a/tests/basics/set_symmetric_difference.py
+++ b/tests/basics/set_symmetric_difference.py
@@ -1,5 +1,5 @@
-print({1,2}.symmetric_difference({2,3}))
-print({1,2}.symmetric_difference([2,3]))
+print(sorted({1,2}.symmetric_difference({2,3})))
+print(sorted({1,2}.symmetric_difference([2,3])))
 s = {1,2}
 print(s.symmetric_difference_update({2,3}))
 l = list(s)
diff --git a/tests/basics/set_union.py b/tests/basics/set_union.py
index 2adcc972c0..572d12f66b 100644
--- a/tests/basics/set_union.py
+++ b/tests/basics/set_union.py
@@ -1 +1 @@
-print({1}.union({2}))
+print(sorted({1}.union({2})))
diff --git a/tests/basics/string_replace.py b/tests/basics/string_replace.py
index a1d0f973bb..8c4c171807 100644
--- a/tests/basics/string_replace.py
+++ b/tests/basics/string_replace.py
@@ -6,3 +6,8 @@ print("aabbaabbaabbaa".replace("aa", "cc", 3))
 print("a".replace("aa", "bb"))
 print("testingtesting".replace("ing", ""))
 print("testINGtesting".replace("ing", "ING!"))
+
+print("".replace("", "1"))
+print("A".replace("", "1"))
+print("AB".replace("", "1"))
+print("AB".replace("", "12"))
diff --git a/tools/pip-micropython b/tools/pip-micropython
index e27e859425..fab8809839 100755
--- a/tools/pip-micropython
+++ b/tools/pip-micropython
@@ -6,6 +6,12 @@
 # ports (if PIP_MICROPY_DEST environment var is set).
 #
 
+if [ "$1" != "install" ]; then
+    echo "Only install command is supported currently"
+    exit 1
+fi
+shift
+
 if [ -n "$PIP_MICROPY_DEST" ]; then
     dest="$PIP_MICROPY_DEST"
     echo "Destination snapshot directory: $dest"