diff --git a/tests/basics/bytes.py b/tests/basics/bytes.py
index ce027e7d19..8f29175506 100644
--- a/tests/basics/bytes.py
+++ b/tests/basics/bytes.py
@@ -33,11 +33,6 @@ print(bytes(3))
 print(bytes([3, 2, 1]))
 print(bytes(range(5)))
 
-def gen():
-    for i in range(4):
-        yield i
-print(bytes(gen()))
-
 # Make sure bytes are not mistreated as unicode
 x = b"\xff\x8e\xfe}\xfd\x7f"
 print(len(x))
diff --git a/tests/basics/bytes_gen.py b/tests/basics/bytes_gen.py
new file mode 100644
index 0000000000..12031ef729
--- /dev/null
+++ b/tests/basics/bytes_gen.py
@@ -0,0 +1,5 @@
+# construct a bytes object from a generator
+def gen():
+    for i in range(4):
+        yield i
+print(bytes(gen()))
diff --git a/tests/extmod/uctypes_ptr_le.py b/tests/extmod/uctypes_ptr_le.py
index ef9890c3f1..4125dd86ff 100644
--- a/tests/extmod/uctypes_ptr_le.py
+++ b/tests/extmod/uctypes_ptr_le.py
@@ -9,7 +9,7 @@ desc = {
 bytes = b"01"
 
 addr = uctypes.addressof(bytes)
-buf = addr.to_bytes(4)
+buf = addr.to_bytes(uctypes.sizeof(desc))
 
 S = uctypes.struct(desc, uctypes.addressof(buf), uctypes.LITTLE_ENDIAN)
 
diff --git a/tests/extmod/uctypes_ptr_native_le.py b/tests/extmod/uctypes_ptr_native_le.py
index 139ed3280c..ba06b26505 100644
--- a/tests/extmod/uctypes_ptr_native_le.py
+++ b/tests/extmod/uctypes_ptr_native_le.py
@@ -15,7 +15,7 @@ desc = {
 bytes = b"01"
 
 addr = uctypes.addressof(bytes)
-buf = addr.to_bytes(4)
+buf = addr.to_bytes(uctypes.sizeof(desc))
 
 S = uctypes.struct(desc, uctypes.addressof(buf), uctypes.NATIVE)
 
diff --git a/tests/run-tests b/tests/run-tests
index a96f3773e4..ff2c418eaf 100755
--- a/tests/run-tests
+++ b/tests/run-tests
@@ -40,19 +40,17 @@ def run_tests(pyb, tests, args):
 
     # Some tests are known to fail on 64-bit machines
     if pyb is None and platform.architecture()[0] == '64bit':
-        skip_tests.add('extmod/uctypes_ptr_le.py')
-        skip_tests.add('extmod/uctypes_ptr_native_le.py')
+        pass
 
     # Some tests are known to fail with native emitter
     # Remove them from the below when they work
     if args.emit == 'native':
-        skip_tests.update({'basics/%s.py' % t for t in 'bytes class_store_class class_super class_super_object closure1 closure2 closure_defargs compare_multi containment del_deref del_local del_name fun3 fun_calldblstar fun_callstar fun_callstardblstar fun_defargs fun_defargs2 fun_kwargs fun_kwonly fun_kwonlydef fun_kwvarargs fun_varargs gen_yield_from gen_yield_from_close gen_yield_from_ducktype gen_yield_from_exc gen_yield_from_iter gen_yield_from_send gen_yield_from_throw generator1 generator2 generator_args generator_close generator_closure generator_exc generator_return generator_send globals_del is_isnot string_format string_join subclass_native2_list subclass_native2_tuple subclass_native3 try2 try_as_var try_finally1 try_finally_loops try_finally_return try_reraise try_reraise2 unary_op unboundlocal with1 with_break with_continue with_return'.split()})
+        skip_tests.update({'basics/%s.py' % t for t in 'bytes_gen class_store_class class_super class_super_object closure1 closure2 closure_defargs compare_multi containment del_deref del_local fun3 fun_calldblstar fun_callstar fun_callstardblstar fun_defargs fun_defargs2 fun_kwargs fun_kwonly fun_kwonlydef fun_kwvarargs fun_varargs gen_yield_from gen_yield_from_close gen_yield_from_ducktype gen_yield_from_exc gen_yield_from_iter gen_yield_from_send gen_yield_from_throw generator1 generator2 generator_args generator_close generator_closure generator_exc generator_return generator_send globals_del is_isnot string_format string_join subclass_native2_list subclass_native2_tuple try2 try_finally1 try_finally_loops try_finally_return try_reraise try_reraise2 unary_op unboundlocal with1 with_break with_continue with_return'.split()})
         skip_tests.add('float/string_format.py')
         skip_tests.add('import/gen_context.py')
         skip_tests.add('import/import_pkg1.py')
         skip_tests.add('io/file_with.py')
         skip_tests.add('micropython/heapalloc.py')
-        skip_tests.add('micropython/viper.py')
         skip_tests.add('misc/features.py')
         skip_tests.add('misc/recursion.py')
         skip_tests.add('misc/rge_sm.py')