diff --git a/extmod/moductypes.c b/extmod/moductypes.c
index 6249a4940..d2d2e85de 100644
--- a/extmod/moductypes.c
+++ b/extmod/moductypes.c
@@ -360,7 +360,7 @@ STATIC void set_aligned(uint val_type, void *p, mp_int_t index, mp_obj_t val) {
         return;
     }
     #endif
-    mp_int_t v = mp_obj_get_int(val);
+    mp_int_t v = mp_obj_get_int_truncated(val);
     switch (val_type) {
         case UINT8:
             ((uint8_t*)p)[index] = (uint8_t)v; return;
diff --git a/py/objint_mpz.c b/py/objint_mpz.c
index 2353bd8d6..d818b6f40 100644
--- a/py/objint_mpz.c
+++ b/py/objint_mpz.c
@@ -116,6 +116,7 @@ mp_obj_t mp_obj_int_from_bytes_impl(bool big_endian, size_t len, const byte *buf
 void mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, size_t len, byte *buf) {
     assert(MP_OBJ_IS_TYPE(self_in, &mp_type_int));
     mp_obj_int_t *self = MP_OBJ_TO_PTR(self_in);
+    memset(buf, 0, len);
     mpz_as_bytes(&self->mpz, big_endian, len, buf);
 }
 
diff --git a/tests/extmod/uctypes_32bit_intbig.py b/tests/extmod/uctypes_32bit_intbig.py
new file mode 100644
index 000000000..a082dc370
--- /dev/null
+++ b/tests/extmod/uctypes_32bit_intbig.py
@@ -0,0 +1,54 @@
+# This test checks previously known problem values for 32-bit ports.
+# It's less useful for 64-bit ports.
+try:
+    import uctypes
+except ImportError:
+    import sys
+    print("SKIP")
+    sys.exit()
+
+buf = b"12345678abcd"
+struct = uctypes.struct(
+    uctypes.addressof(buf),
+    {"f32": uctypes.UINT32 | 0, "f64": uctypes.UINT64 | 4},
+    uctypes.LITTLE_ENDIAN
+)
+
+struct.f32 = 0x7fffffff
+print(buf)
+
+struct.f32 = 0x80000000
+print(buf)
+
+struct.f32 = 0xff010203
+print(buf)
+
+struct.f64 = 0x80000000
+print(buf)
+
+struct.f64 = 0x80000000 * 2
+print(buf)
+
+print("=")
+
+buf = b"12345678abcd"
+struct = uctypes.struct(
+    uctypes.addressof(buf),
+    {"f32": uctypes.UINT32 | 0, "f64": uctypes.UINT64 | 4},
+    uctypes.BIG_ENDIAN
+)
+
+struct.f32 = 0x7fffffff
+print(buf)
+
+struct.f32 = 0x80000000
+print(buf)
+
+struct.f32 = 0xff010203
+print(buf)
+
+struct.f64 = 0x80000000
+print(buf)
+
+struct.f64 = 0x80000000 * 2
+print(buf)
diff --git a/tests/extmod/uctypes_32bit_intbig.py.exp b/tests/extmod/uctypes_32bit_intbig.py.exp
new file mode 100644
index 000000000..d1fc1fe35
--- /dev/null
+++ b/tests/extmod/uctypes_32bit_intbig.py.exp
@@ -0,0 +1,11 @@
+b'\xff\xff\xff\x7f5678abcd'
+b'\x00\x00\x00\x805678abcd'
+b'\x03\x02\x01\xff5678abcd'
+b'\x03\x02\x01\xff\x00\x00\x00\x80\x00\x00\x00\x00'
+b'\x03\x02\x01\xff\x00\x00\x00\x00\x01\x00\x00\x00'
+=
+b'\x7f\xff\xff\xff5678abcd'
+b'\x80\x00\x00\x005678abcd'
+b'\xff\x01\x02\x035678abcd'
+b'\xff\x01\x02\x03\x00\x00\x00\x00\x80\x00\x00\x00'
+b'\xff\x01\x02\x03\x00\x00\x00\x01\x00\x00\x00\x00'