diff --git a/src/util/mpq.cpp b/src/util/mpq.cpp
index 6bfd157c4..c52496c4f 100644
--- a/src/util/mpq.cpp
+++ b/src/util/mpq.cpp
@@ -34,7 +34,7 @@ mpz floor(mpq const & a) {
     mpz r;
     mpz_tdiv_q(mpq::zval(r), mpq_numref(a.m_val), mpq_denref(a.m_val));
     if (a.is_neg())
-        r -= 1;
+        --r;
     return r;
 }
 
@@ -44,7 +44,7 @@ mpz ceil(mpq const & a) {
     mpz r;
     mpz_tdiv_q(mpq::zval(r), mpq_numref(a.m_val), mpq_denref(a.m_val));
     if (a.is_pos())
-        r += 1;
+        ++r;
     return r;
 }
 
diff --git a/src/util/mpz.h b/src/util/mpz.h
index cfbe2587e..7be07ebc7 100644
--- a/src/util/mpz.h
+++ b/src/util/mpz.h
@@ -79,6 +79,11 @@ public:
     DEFINE_ARITH_OPS(mpz)
     friend mpz operator%(mpz const & a, mpz const & b);
 
+    mpz & operator++() { return operator+=(1); }
+    mpz & operator--() { return operator-=(1); }
+    mpz operator++(int) { mpz r(*this); ++(*this); return r; }
+    mpz operator--(int) { mpz r(*this); --(*this); return r; }
+
     mpz & operator&=(mpz const & o) { mpz_and(m_val, m_val, o.m_val); return *this; }
     mpz & operator|=(mpz const & o) { mpz_ior(m_val, m_val, o.m_val); return *this; }
     mpz & operator^=(mpz const & o) { mpz_xor(m_val, m_val, o.m_val); return *this; }