diff --git a/src/network/test-networkd-conf.c b/src/network/test-networkd-conf.c
index 2007acb781..5d338e6f1a 100644
--- a/src/network/test-networkd-conf.c
+++ b/src/network/test-networkd-conf.c
@@ -101,7 +101,7 @@ static void test_config_parse_duid_rawdata(void) {
         test_config_parse_duid_rawdata_one("11::", 0, &(DUID){0, 1, {0x11}});  /* FIXME: should this be an error? */
         test_config_parse_duid_rawdata_one("abcdef", 0, &(DUID){});
         test_config_parse_duid_rawdata_one(BYTES_0_128, 0, &(DUID){});
-        test_config_parse_duid_rawdata_one(BYTES_0_128 + 2, 0, &(DUID){0, 128, BYTES_1_128});
+        test_config_parse_duid_rawdata_one(&BYTES_0_128[2], 0, &(DUID){0, 128, BYTES_1_128});
 }
 
 static void test_config_parse_hwaddr(void) {
diff --git a/src/test/test-alloc-util.c b/src/test/test-alloc-util.c
index d85f705504..72356aeaa4 100644
--- a/src/test/test-alloc-util.c
+++ b/src/test/test-alloc-util.c
@@ -136,6 +136,9 @@ static void test_cleanup_order(void) {
 static void test_auto_erase_memory(void) {
         _cleanup_(erase_and_freep) uint8_t *p1, *p2;
 
+        /* print address of p2, else e.g. clang-11 will optimize it out */
+        log_debug("p1: %p p2: %p", &p1, &p2);
+
         assert_se(p1 = new(uint8_t, 1024));
         assert_se(p2 = new(uint8_t, 1024));
 
diff --git a/src/test/test-clock.c b/src/test/test-clock.c
index e5a3de8a59..271d465546 100644
--- a/src/test/test-clock.c
+++ b/src/test/test-clock.c
@@ -49,7 +49,7 @@ static void test_clock_is_localtime(void) {
                 log_info("scenario #%zu:, expected result %i", i, scenarios[i].expected_result);
                 log_info("%s", scenarios[i].contents);
                 rewind(f);
-                ftruncate(fileno(f), 0);
+                assert_se(ftruncate(fileno(f), 0) == 0);
                 assert_se(write_string_stream(f, scenarios[i].contents, WRITE_STRING_FILE_AVOID_NEWLINE) == 0);
                 assert_se(clock_is_localtime(adjtime) == scenarios[i].expected_result);
         }