diff --git a/contrib/scripts/nm-ci-run.sh b/contrib/scripts/nm-ci-run.sh
index 14a4a2fe53..22450d40c7 100755
--- a/contrib/scripts/nm-ci-run.sh
+++ b/contrib/scripts/nm-ci-run.sh
@@ -201,7 +201,7 @@ run_autotools() {
             _print_test_logs "first-test"
 
             echo ">>>> RUN SECOND TEST (start)"
-            NMTST_DEBUG=TRACE,no-expect-message make check -k || :
+            NMTST_DEBUG="debug,TRACE,no-expect-message" make check -k || :
             echo ">>>> RUN SECOND TEST (done)"
 
             _print_test_logs "second-test"
diff --git a/src/libnm-glib-aux/nm-test-utils.h b/src/libnm-glib-aux/nm-test-utils.h
index b35eeb4b09..41e1a6cedf 100644
--- a/src/libnm-glib-aux/nm-test-utils.h
+++ b/src/libnm-glib-aux/nm-test-utils.h
@@ -772,6 +772,12 @@ nmtst_init(int *argc, char ***argv, gboolean assert_logging)
 static inline gboolean
 nmtst_is_debug(void)
 {
+    /* This is based on the "debug"/"no-debug" flag in "$NMTST_DEBUG".
+     *
+     * If debugging is enabled, print more information. However, make sure
+     * that the test behaves still in a similar manner and that the same code
+     * path are taken where it matters (it matters for example, if the code path
+     * consumes random numbers). */
     g_assert(nmtst_initialized());
     return __nmtst_internal.is_debug;
 }