diff --git a/tests/suites/test_suite_ecdsa.function b/tests/suites/test_suite_ecdsa.function
index e7aeb07..5e4cdaa 100644
--- a/tests/suites/test_suite_ecdsa.function
+++ b/tests/suites/test_suite_ecdsa.function
@@ -82,13 +82,14 @@
 {
     mbedtls_ecp_group grp;
     mbedtls_ecp_point Q;
-    mbedtls_mpi d, r, s, r_check, s_check;
+    mbedtls_mpi d, r, s, r_check, s_check, zero;
     mbedtls_test_rnd_buf_info rnd_info;
 
     mbedtls_ecp_group_init( &grp );
     mbedtls_ecp_point_init( &Q );
     mbedtls_mpi_init( &d ); mbedtls_mpi_init( &r ); mbedtls_mpi_init( &s );
     mbedtls_mpi_init( &r_check ); mbedtls_mpi_init( &s_check );
+    mbedtls_mpi_init( &zero );
 
     TEST_ASSERT( mbedtls_ecp_group_load( &grp, id ) == 0 );
     TEST_ASSERT( mbedtls_ecp_point_read_string( &Q, 16, xQ_str, yQ_str ) == 0 );
@@ -117,7 +118,7 @@
 
     if ( result == 0)
     {
-        /* save correct values; we'll generate incorrect ones below */
+        /* Check we generated the expected values */
         TEST_EQUAL( mbedtls_mpi_cmp_mpi( &r, &r_check ), 0 );
         TEST_EQUAL( mbedtls_mpi_cmp_mpi( &s, &s_check ), 0 );
 
@@ -130,8 +131,8 @@
                     &grp.G, &r_check, &s_check ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
 
         /* Invalid signatures: r or s or both one off */
-        TEST_EQUAL( mbedtls_mpi_sub_int( &r, &r, 1 ), 0 );
-        TEST_EQUAL( mbedtls_mpi_add_int( &s, &s, 1 ), 0 );
+        TEST_EQUAL( mbedtls_mpi_sub_int( &r, &r_check, 1 ), 0 );
+        TEST_EQUAL( mbedtls_mpi_add_int( &s, &s_check, 1 ), 0 );
 
         TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
                     &r, &s_check ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
@@ -141,30 +142,26 @@
                     &r, &s ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
 
         /* Invalid signatures: r, s or both (CVE-2022-21449) are zero */
-        TEST_EQUAL( mbedtls_mpi_lset( &r, 0 ), 0 );
-        TEST_EQUAL( mbedtls_mpi_lset( &s, 0 ), 0 );
+        TEST_EQUAL( mbedtls_mpi_lset( &zero, 0 ), 0 );
 
         TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
-                    &r, &s_check ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
+                    &zero, &s_check ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
         TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
-                    &r_check, &s ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
+                    &r_check, &zero ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
         TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
-                    &r, &s ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
-
-        /* Invalid signatures: r, s or both are negative */
-        TEST_EQUAL( mbedtls_mpi_lset( &r, -1 ), 0 );
-        TEST_EQUAL( mbedtls_mpi_lset( &s, -1 ), 0 );
-
-        TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
-                    &r, &s_check ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
-        TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
-                    &r_check, &s ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
-        TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
-                    &r, &s ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
+                    &zero, &zero ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
 
         /* Invalid signatures: r, s or both are == N */
-        TEST_EQUAL( mbedtls_mpi_copy( &r, &grp.N ), 0 );
-        TEST_EQUAL( mbedtls_mpi_copy( &s, &grp.N ), 0 );
+        TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
+                    &grp.N, &s_check ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
+        TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
+                    &r_check, &grp.N ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
+        TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
+                    &grp.N, &grp.N ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
+
+        /* Invalid signatures: r, s or both are negative */
+        TEST_EQUAL( mbedtls_mpi_sub_mpi( &r, &r_check, &grp.N ), 0 );
+        TEST_EQUAL( mbedtls_mpi_sub_mpi( &s, &s_check, &grp.N ), 0 );
 
         TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
                     &r, &s_check ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
@@ -174,8 +171,8 @@
                     &r, &s ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
 
         /* Invalid signatures: r or s or both are > N */
-        TEST_EQUAL( mbedtls_mpi_add_int( &r, &grp.N, 1 ), 0 );
-        TEST_EQUAL( mbedtls_mpi_add_int( &s, &grp.N, 1 ), 0 );
+        TEST_EQUAL( mbedtls_mpi_add_mpi( &r, &r_check, &grp.N ), 0 );
+        TEST_EQUAL( mbedtls_mpi_add_mpi( &s, &s_check, &grp.N ), 0 );
 
         TEST_EQUAL( mbedtls_ecdsa_verify( &grp, hash->x, hash->len, &Q,
                     &r, &s_check ), MBEDTLS_ERR_ECP_VERIFY_FAILED );
@@ -190,6 +187,7 @@
     mbedtls_ecp_point_free( &Q );
     mbedtls_mpi_free( &d ); mbedtls_mpi_free( &r ); mbedtls_mpi_free( &s );
     mbedtls_mpi_free( &r_check ); mbedtls_mpi_free( &s_check );
+    mbedtls_mpi_free( &zero );
 }
 /* END_CASE */