diff --git a/tests/suites/test_suite_constant_time.function b/tests/suites/test_suite_constant_time.function
index 14dc8ae5cd..a2bf3967f5 100644
--- a/tests/suites/test_suite_constant_time.function
+++ b/tests/suites/test_suite_constant_time.function
@@ -18,7 +18,7 @@
 /* BEGIN_CASE */
 void mbedtls_ct_memcmp_null()
 {
-    uint32_t x;
+    uint32_t x = 0;
     TEST_ASSERT(mbedtls_ct_memcmp(&x, NULL, 0) == 0);
     TEST_ASSERT(mbedtls_ct_memcmp(NULL, &x, 0) == 0);
     TEST_ASSERT(mbedtls_ct_memcmp(NULL, NULL, 0) == 0);