diff --git a/math/magic_number.cpp b/math/magic_number.cpp
index 0d1fc3711..3765b69e3 100644
--- a/math/magic_number.cpp
+++ b/math/magic_number.cpp
@@ -50,7 +50,7 @@ bool magic_number(int n) {
  */
 static void tests() {
     std::cout << "Test 1:\t n=60\n";
-    assert(magic_number(60) == false);
+    assert(math::magic_number(60) == false);
     std::cout << "passed\n";
 
     std::cout << "Test 2:\t n=730\n";