diff --git a/py/argcheck.c b/py/argcheck.c
index 2a606d613aa67..a5ba0fbf69b50 100644
--- a/py/argcheck.c
+++ b/py/argcheck.c
@@ -32,7 +32,9 @@
 void mp_arg_check_num(size_t n_args, size_t n_kw, size_t n_args_min, size_t n_args_max, bool takes_kw) {
     // NOTE(tannewt): This prevents this function from being optimized away.
     // Without it, functions can crash when reading invalid args.
+#ifdef __GNUC__
     __asm volatile ("");
+#endif
     // TODO maybe take the function name as an argument so we can print nicer error messages
 
     if (n_kw && !takes_kw) {
diff --git a/py/nlr.h b/py/nlr.h
index 8fa6eb950d58f..9a7b81e297637 100644
--- a/py/nlr.h
+++ b/py/nlr.h
@@ -55,6 +55,7 @@ struct _nlr_buf_t {
 #elif defined(__xtensa__)
     void *regs[10];
 #else
+    #undef MICROPY_NLR_SETJMP
     #define MICROPY_NLR_SETJMP (1)
     //#warning "No native NLR support for this arch, using setjmp implementation"
 #endif
diff --git a/py/persistentcode.c b/py/persistentcode.c
index ba126a3fb254c..7aec46ac59385 100644
--- a/py/persistentcode.c
+++ b/py/persistentcode.c
@@ -124,7 +124,11 @@ STATIC size_t read_uint(mp_reader_t *reader) {
 
 STATIC qstr load_qstr(mp_reader_t *reader) {
     size_t len = read_uint(reader);
+#ifdef __GNUC__
     char str[len];
+#else
+    char *str = alloca(len);
+#endif
     read_bytes(reader, (byte*)str, len);
     qstr qst = qstr_from_strn(str, len);
     return qst;
diff --git a/py/stackctrl.c b/py/stackctrl.c
index b4ec15b0da1a3..3244c871a112a 100644
--- a/py/stackctrl.c
+++ b/py/stackctrl.c
@@ -29,7 +29,9 @@
 
 void mp_stack_ctrl_init(void) {
     // Force routine to not be inlined. Better guarantee than MP_NOINLINE for -flto.
+#ifdef __GNUC__
     __asm volatile ("");
+#endif
     volatile int stack_dummy;
     MP_STATE_THREAD(stack_top) = (char*)&stack_dummy;
 }
@@ -41,7 +43,9 @@ void mp_stack_set_top(void *top) {
 mp_uint_t mp_stack_usage(void) {
     // Assumes descending stack
     // Force routine to not be inlined. Better guarantee than MP_NOINLINE for -flto.
+#ifdef __GNUC__
     __asm volatile ("");
+#endif
     volatile int stack_dummy;
     return MP_STATE_THREAD(stack_top) - (char*)&stack_dummy;
 }
diff --git a/tests/run-tests b/tests/run-tests
index f1035c4353e91..109dfb8a7b5d4 100755
--- a/tests/run-tests
+++ b/tests/run-tests
@@ -389,7 +389,10 @@ def run_tests(pyb, tests, args, base_path="."):
             # run CPython to work out expected output
             e = {"PYTHONPATH": os.getcwd(),
                  "PATH": os.environ["PATH"],
-                 "LANG": "en_US.UTF-8"}
+                 "LANG": "en_US.UTF-8",
+                 "PYTHONIOENCODING": "utf-8"}
+            if 'SYSTEMROOT' in os.environ:
+                e['SYSTEMROOT'] = os.environ['SYSTEMROOT']
             p = subprocess.Popen([CPYTHON3, '-B', test_file], env=e, stdout=subprocess.PIPE)
             output_expected = b''
             while p.poll() is None: