diff --git a/src/util/mpz.cpp b/src/util/mpz.cpp
index bdad1ddfe..736b401b8 100644
--- a/src/util/mpz.cpp
+++ b/src/util/mpz.cpp
@@ -1842,7 +1842,7 @@ std::string mpz_manager<SYNCH>::to_string(mpz const & a) const {
 template<bool SYNCH>
 unsigned mpz_manager<SYNCH>::hash(mpz const & a) {
     if (is_small(a))
-        return a.m_val;
+        return ::abs(a.m_val);
 #ifndef _MP_GMP
     unsigned sz = size(a);
     if (sz == 1)