diff --git a/src/util/mpz.h b/src/util/mpz.h
index e74da812a..f6ed99689 100644
--- a/src/util/mpz.h
+++ b/src/util/mpz.h
@@ -605,7 +605,11 @@ public:
     void set(mpz & a, unsigned val) { set(a, (uint64_t)val); }
 
     void set(mpz & a, int64_t val) {
-        if (mpz::fits_in_small(val) && is_small(a)) {
+        if (val == 0) {
+            // Zero is always represented as small
+            reset(a);
+        }
+        else if (mpz::fits_in_small(val) && is_small(a)) {
             a.set(val);
         }
         else {
@@ -614,7 +618,11 @@ public:
     }
 
     void set(mpz & a, uint64_t val) {
-        if (mpz::fits_in_small(val) && is_small(a)) {
+        if (val == 0) {
+            // Zero is always represented as small
+            reset(a);
+        }
+        else if (mpz::fits_in_small(val) && is_small(a)) {
             a.set(static_cast<int64_t>(val));
         }
         else {