diff --git a/extmod/moductypes.c b/extmod/moductypes.c
index f1108649aa..97e8d7a787 100644
--- a/extmod/moductypes.c
+++ b/extmod/moductypes.c
@@ -47,6 +47,7 @@
 #define BITF_LEN_BITS 5
 #define BITF_OFF_BITS 5
 #define OFFSET_BITS 17
+#define LEN_BITS (OFFSET_BITS + BITF_OFF_BITS)
 #if VAL_TYPE_BITS + BITF_LEN_BITS + BITF_OFF_BITS + OFFSET_BITS != 31
 #error Invalid encoding field length
 #endif
@@ -409,9 +410,9 @@ STATIC mp_obj_t uctypes_struct_attr_op(mp_obj_t self_in, qstr attr, mp_obj_t set
                 }
             }
         } else if (val_type >= BFUINT8 && val_type <= BFINT32) {
-            uint bit_offset = (offset >> 17) & 31;
-            uint bit_len = (offset >> 22) & 31;
-            offset &= (1 << 17) - 1;
+            uint bit_offset = (offset >> OFFSET_BITS) & 31;
+            uint bit_len = (offset >> LEN_BITS) & 31;
+            offset &= (1 << OFFSET_BITS) - 1;
             mp_uint_t val;
             if (self->flags == LAYOUT_NATIVE) {
                 val = get_aligned_basic(val_type & 6, self->addr + offset);
@@ -663,51 +664,51 @@ STATIC const mp_rom_map_elem_t mp_module_uctypes_globals_table[] = {
 
     { MP_ROM_QSTR(MP_QSTR_VOID), MP_ROM_INT(TYPE2SMALLINT(UINT8, VAL_TYPE_BITS)) },
 
-    { MP_ROM_QSTR(MP_QSTR_UINT8), MP_ROM_INT(TYPE2SMALLINT(UINT8, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_INT8), MP_ROM_INT(TYPE2SMALLINT(INT8, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_UINT16), MP_ROM_INT(TYPE2SMALLINT(UINT16, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_INT16), MP_ROM_INT(TYPE2SMALLINT(INT16, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_UINT32), MP_ROM_INT(TYPE2SMALLINT(UINT32, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_INT32), MP_ROM_INT(TYPE2SMALLINT(INT32, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_UINT64), MP_ROM_INT(TYPE2SMALLINT(UINT64, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_INT64), MP_ROM_INT(TYPE2SMALLINT(INT64, 4)) },
+    { MP_ROM_QSTR(MP_QSTR_UINT8), MP_ROM_INT(TYPE2SMALLINT(UINT8, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_INT8), MP_ROM_INT(TYPE2SMALLINT(INT8, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_UINT16), MP_ROM_INT(TYPE2SMALLINT(UINT16, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_INT16), MP_ROM_INT(TYPE2SMALLINT(INT16, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_UINT32), MP_ROM_INT(TYPE2SMALLINT(UINT32, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_INT32), MP_ROM_INT(TYPE2SMALLINT(INT32, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_UINT64), MP_ROM_INT(TYPE2SMALLINT(UINT64, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_INT64), MP_ROM_INT(TYPE2SMALLINT(INT64, VAL_TYPE_BITS)) },
 
-    { MP_ROM_QSTR(MP_QSTR_BFUINT8), MP_ROM_INT(TYPE2SMALLINT(BFUINT8, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_BFINT8), MP_ROM_INT(TYPE2SMALLINT(BFINT8, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_BFUINT16), MP_ROM_INT(TYPE2SMALLINT(BFUINT16, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_BFINT16), MP_ROM_INT(TYPE2SMALLINT(BFINT16, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_BFUINT32), MP_ROM_INT(TYPE2SMALLINT(BFUINT32, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_BFINT32), MP_ROM_INT(TYPE2SMALLINT(BFINT32, 4)) },
+    { MP_ROM_QSTR(MP_QSTR_BFUINT8), MP_ROM_INT(TYPE2SMALLINT(BFUINT8, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_BFINT8), MP_ROM_INT(TYPE2SMALLINT(BFINT8, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_BFUINT16), MP_ROM_INT(TYPE2SMALLINT(BFUINT16, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_BFINT16), MP_ROM_INT(TYPE2SMALLINT(BFINT16, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_BFUINT32), MP_ROM_INT(TYPE2SMALLINT(BFUINT32, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_BFINT32), MP_ROM_INT(TYPE2SMALLINT(BFINT32, VAL_TYPE_BITS)) },
 
-    { MP_ROM_QSTR(MP_QSTR_BF_POS), MP_ROM_INT(17) },
-    { MP_ROM_QSTR(MP_QSTR_BF_LEN), MP_ROM_INT(22) },
+    { MP_ROM_QSTR(MP_QSTR_BF_POS), MP_ROM_INT(OFFSET_BITS) },
+    { MP_ROM_QSTR(MP_QSTR_BF_LEN), MP_ROM_INT(LEN_BITS) },
 
     #if MICROPY_PY_BUILTINS_FLOAT
-    { MP_ROM_QSTR(MP_QSTR_FLOAT32), MP_ROM_INT(TYPE2SMALLINT(FLOAT32, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_FLOAT64), MP_ROM_INT(TYPE2SMALLINT(FLOAT64, 4)) },
+    { MP_ROM_QSTR(MP_QSTR_FLOAT32), MP_ROM_INT(TYPE2SMALLINT(FLOAT32, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_FLOAT64), MP_ROM_INT(TYPE2SMALLINT(FLOAT64, VAL_TYPE_BITS)) },
     #endif
 
     #if MICROPY_PY_UCTYPES_NATIVE_C_TYPES
     // C native type aliases. These depend on GCC-compatible predefined
     // preprocessor macros.
     #if __SIZEOF_SHORT__ == 2
-    { MP_ROM_QSTR(MP_QSTR_SHORT), MP_ROM_INT(TYPE2SMALLINT(INT16, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_USHORT), MP_ROM_INT(TYPE2SMALLINT(UINT16, 4)) },
+    { MP_ROM_QSTR(MP_QSTR_SHORT), MP_ROM_INT(TYPE2SMALLINT(INT16, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_USHORT), MP_ROM_INT(TYPE2SMALLINT(UINT16, VAL_TYPE_BITS)) },
     #endif
     #if __SIZEOF_INT__ == 4
-    { MP_ROM_QSTR(MP_QSTR_INT), MP_ROM_INT(TYPE2SMALLINT(INT32, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_UINT), MP_ROM_INT(TYPE2SMALLINT(UINT32, 4)) },
+    { MP_ROM_QSTR(MP_QSTR_INT), MP_ROM_INT(TYPE2SMALLINT(INT32, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_UINT), MP_ROM_INT(TYPE2SMALLINT(UINT32, VAL_TYPE_BITS)) },
     #endif
     #if __SIZEOF_LONG__ == 4
-    { MP_ROM_QSTR(MP_QSTR_LONG), MP_ROM_INT(TYPE2SMALLINT(INT32, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_ULONG), MP_ROM_INT(TYPE2SMALLINT(UINT32, 4)) },
+    { MP_ROM_QSTR(MP_QSTR_LONG), MP_ROM_INT(TYPE2SMALLINT(INT32, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_ULONG), MP_ROM_INT(TYPE2SMALLINT(UINT32, VAL_TYPE_BITS)) },
     #elif __SIZEOF_LONG__ == 8
-    { MP_ROM_QSTR(MP_QSTR_LONG), MP_ROM_INT(TYPE2SMALLINT(INT64, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_ULONG), MP_ROM_INT(TYPE2SMALLINT(UINT64, 4)) },
+    { MP_ROM_QSTR(MP_QSTR_LONG), MP_ROM_INT(TYPE2SMALLINT(INT64, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_ULONG), MP_ROM_INT(TYPE2SMALLINT(UINT64, VAL_TYPE_BITS)) },
     #endif
     #if __SIZEOF_LONG_LONG__ == 8
-    { MP_ROM_QSTR(MP_QSTR_LONGLONG), MP_ROM_INT(TYPE2SMALLINT(INT64, 4)) },
-    { MP_ROM_QSTR(MP_QSTR_ULONGLONG), MP_ROM_INT(TYPE2SMALLINT(UINT64, 4)) },
+    { MP_ROM_QSTR(MP_QSTR_LONGLONG), MP_ROM_INT(TYPE2SMALLINT(INT64, VAL_TYPE_BITS)) },
+    { MP_ROM_QSTR(MP_QSTR_ULONGLONG), MP_ROM_INT(TYPE2SMALLINT(UINT64, VAL_TYPE_BITS)) },
     #endif
     #endif // MICROPY_PY_UCTYPES_NATIVE_C_TYPES