diff --git a/include/heyoka/number.hpp b/include/heyoka/number.hpp
index 478e846f6..8c3d9d17f 100644
--- a/include/heyoka/number.hpp
+++ b/include/heyoka/number.hpp
@@ -105,6 +105,7 @@ HEYOKA_DLL_PUBLIC bool is_negative_one(const number &);
 HEYOKA_DLL_PUBLIC bool is_negative(const number &);
 HEYOKA_DLL_PUBLIC bool is_integer(const number &);
 
+HEYOKA_DLL_PUBLIC number operator+(number);
 HEYOKA_DLL_PUBLIC number operator-(const number &);
 
 HEYOKA_DLL_PUBLIC number operator+(const number &, const number &);
diff --git a/test/number.cpp b/test/number.cpp
index 7323dffaf..d998917bd 100644
--- a/test/number.cpp
+++ b/test/number.cpp
@@ -928,3 +928,34 @@ TEST_CASE("move semantics")
     REQUIRE(x3 == number{3.});
     REQUIRE(x2 == number{0.});
 }
+
+TEST_CASE("basic arith")
+{
+    number n{42.};
+
+    REQUIRE(+n == n);
+    REQUIRE(-n == number{-42.});
+}
+
+TEST_CASE("copy assignment")
+{
+    number n1{42.};
+    number n2{42.f};
+
+    n2 = n1;
+
+    REQUIRE(n2 == number{42.});
+}
+
+TEST_CASE("swap")
+{
+    REQUIRE(std::is_nothrow_swappable_v<number>);
+
+    number n1{42.};
+    number n2{42.f};
+
+    swap(n1, n2);
+
+    REQUIRE(n2 == number{42.});
+    REQUIRE(n1 == number{42.f});
+}