diff --git a/src/util/rational.h b/src/util/rational.h
index 3649a9848..ba99f308e 100644
--- a/src/util/rational.h
+++ b/src/util/rational.h
@@ -50,7 +50,7 @@ public:
 
     explicit rational(unsigned n) { m().set(m_val, n); }
       
-    rational(int n, int d) { m().set(m_val, n, d); }
+    rational(int64_t n, int d) { m().set(m_val, n, d); }
     rational(mpq const & q) { m().set(m_val, q); }
     rational(mpq && q) noexcept : m_val(std::move(q)) {}
     rational(mpz const & z) { m().set(m_val, z); }