1 files changed, 19 insertions, 1 deletions
diff --git a/py/objint_longlong.c b/py/objint_longlong.c
index ee499e026..00fe5636c 100644
--- a/py/objint_longlong.c
+++ b/py/objint_longlong.c
@@ -57,10 +57,27 @@ mp_obj_t mp_obj_int_from_bytes_impl(bool big_endian, size_t len, const byte *buf
     return mp_obj_new_int_from_ll(value);
 }
 
-void mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, size_t len, byte *buf) {
+bool mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, size_t len, byte *buf) {
     assert(mp_obj_is_exact_type(self_in, &mp_type_int));
     mp_obj_int_t *self = self_in;
     long long val = self->val;
+    size_t slen; // Number of bytes to represent val
+
+    // This logic has a twin in objint.c
+    if (val > 0) {
+        slen = (sizeof(long long) * 8 - mp_clzll(val) + 7) / 8;
+    } else if (val < -1) {
+        slen = (sizeof(long long) * 8 - mp_clzll(~val) + 8) / 8;
+    } else {
+        // clz of 0 is defined, so 0 and -1 map to 0 and 1
+        slen = -val;
+    }
+
+    if (slen > len) {
+        return false; // Would overflow
+        // TODO: Determine whether to copy and truncate, as some callers probably expect this...?
+    }
+
     if (big_endian) {
         byte *b = buf + len;
         while (b > buf) {
@@ -73,6 +90,7 @@ void mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, size_t len, byt
             val >>= 8;
         }
     }
+    return true;
 }
 
 int mp_obj_int_sign(mp_obj_t self_in) {