diff --git a/.travis.yml b/.travis.yml
index d8a5973e..f39da33b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,7 +6,7 @@ dist: trusty
 
 matrix:
   include:
-   - php: 5.3
+   - php: 5.3 # Composer requires PHP 5.3.2+ to run, so we cannot test below 5.3
      dist: precise # PHP 5.3 is supported only on Precise.
    - php: 5.4
    - php: 5.5
@@ -16,7 +16,7 @@ matrix:
    - php: 7.2
    - php: 7.3
    - php: 7.4
-   - php: nightly
+#   - php: nightly # PHP nightly build testing disabled because PHPUnit doesn't support PHP8 yet.
   fast_finish: true
   allow_failures:
    - php: nightly