diff --git a/src/util/rational.h b/src/util/rational.h
index 803c562ad..392a1982b 100644
--- a/src/util/rational.h
+++ b/src/util/rational.h
@@ -41,6 +41,7 @@ public:
     rational() {}
     
     rational(rational const & r) { m().set(m_val, r.m_val); }
+    rational(rational && r) : m_val(std::move(r.m_val)) {}
 
     explicit rational(int n) { m().set(m_val, n); }