diff --git a/py/mpz.c b/py/mpz.c
index c0a3d4b..a056a6e 100644
--- a/py/mpz.c
+++ b/py/mpz.c
@@ -820,6 +820,10 @@
 }
 
 int mpz_cmp(const mpz_t *z1, const mpz_t *z2) {
+    // to catch comparison of -0 with +0
+    if (z1->len == 0 && z2->len == 0) {
+        return 0;
+    }
     int cmp = (int)z2->neg - (int)z1->neg;
     if (cmp != 0) {
         return cmp;