diff --git a/tests/cbmc/proofs/s2n_stuffer_peek_check_for_str/s2n_stuffer_peek_check_for_str_harness.c b/tests/cbmc/proofs/s2n_stuffer_peek_check_for_str/s2n_stuffer_peek_check_for_str_harness.c
index 77a1ab329d4..07de8a3fe93 100644
--- a/tests/cbmc/proofs/s2n_stuffer_peek_check_for_str/s2n_stuffer_peek_check_for_str_harness.c
+++ b/tests/cbmc/proofs/s2n_stuffer_peek_check_for_str/s2n_stuffer_peek_check_for_str_harness.c
@@ -37,7 +37,7 @@ void s2n_stuffer_peek_check_for_str_harness()
     size_t expected_length = (expected != NULL) ? strlen(expected) : 0;
     if (expected_length > 0 && s2n_stuffer_peek_check_for_str(stuffer, expected) == S2N_SUCCESS) {
         uint8_t *actual = stuffer->blob.data + stuffer->read_cursor;
-        assert(!memcmp(actual, expected, expected_length));
+        assert(s2n_constant_time_equals(actual, (uint8_t *) expected, expected_length));
     }
     assert_stuffer_equivalence(stuffer, &old_stuffer, &old_byte_from_stuffer);
     assert(s2n_result_is_ok(s2n_stuffer_validate(stuffer)));
diff --git a/tests/cbmc/proofs/s2n_stuffer_read_expected_str/s2n_stuffer_read_expected_str_harness.c b/tests/cbmc/proofs/s2n_stuffer_read_expected_str/s2n_stuffer_read_expected_str_harness.c
index 076da691da5..3a6b73caa42 100644
--- a/tests/cbmc/proofs/s2n_stuffer_read_expected_str/s2n_stuffer_read_expected_str_harness.c
+++ b/tests/cbmc/proofs/s2n_stuffer_read_expected_str/s2n_stuffer_read_expected_str_harness.c
@@ -37,7 +37,7 @@ void s2n_stuffer_read_expected_str_harness()
     size_t expected_length = (expected != NULL) ? strlen(expected) : 0;
     if (expected_length > 0 && s2n_stuffer_read_expected_str(stuffer, expected) == S2N_SUCCESS) {
         uint8_t *actual = stuffer->blob.data + stuffer->read_cursor - expected_length;
-        assert(!memcmp(actual, expected, expected_length));
+        assert(s2n_constant_time_equals(actual, (uint8_t *) expected, expected_length));
         assert(stuffer->read_cursor == old_stuffer.read_cursor + expected_length);
     } else {
         assert(stuffer->read_cursor == old_stuffer.read_cursor);