diff --git a/tests/suites/test_suite_ecdsa.function b/tests/suites/test_suite_ecdsa.function
index 7f89952..7107832 100644
--- a/tests/suites/test_suite_ecdsa.function
+++ b/tests/suites/test_suite_ecdsa.function
@@ -14,7 +14,7 @@
     mbedtls_ecp_point Q;
     mbedtls_mpi d, r, s;
     rnd_pseudo_info rnd_info;
-    unsigned char buf[66];
+    unsigned char buf[MBEDTLS_MD_MAX_SIZE];
 
     mbedtls_ecp_group_init( &grp );
     mbedtls_ecp_point_init( &Q );