diff --git a/math/sieve_of_eratosthenes.cpp b/math/sieve_of_eratosthenes.cpp
index 7b77b3474..e252e1955 100644
--- a/math/sieve_of_eratosthenes.cpp
+++ b/math/sieve_of_eratosthenes.cpp
@@ -56,7 +56,7 @@ void print(uint32_t N, const std::vector<bool> &is_prime) {
 /**
  * Test implementations
  */
-void tests() {
+static void tests() {
     //                    0      1      2     3     4      5     6      7     8
     //                    9      10
     std::vector<bool> ans{false, false, true,  true,  false, true,