diff --git a/py/objfloat.c b/py/objfloat.c
index e4d5a6570..31c624778 100644
--- a/py/objfloat.c
+++ b/py/objfloat.c
@@ -88,7 +88,7 @@ typedef uint32_t mp_float_uint_t;
         if (adj_exp <= MP_FLOAT_FRAC_BITS) {
             // number may have a fraction; xor the integer part with the fractional part
             val = (frc >> (MP_FLOAT_FRAC_BITS - adj_exp))
-                ^ (frc & ((1 << (MP_FLOAT_FRAC_BITS - adj_exp)) - 1));
+                ^ (frc & (((mp_float_uint_t)1 << (MP_FLOAT_FRAC_BITS - adj_exp)) - 1));
         } else if ((unsigned int)adj_exp < BITS_PER_BYTE * sizeof(mp_int_t) - 1) {
             // the number is a (big) whole integer and will fit in val's signed-width
             val = (mp_int_t)frc << (adj_exp - MP_FLOAT_FRAC_BITS);