diff --git a/README.md b/README.md
index 6ec8a67..1b1c916 100644
--- a/README.md
+++ b/README.md
@@ -68,6 +68,9 @@ the name would be `ruby-3.0-golang-1.15-git-2.29`.
 1. Add a test task: `ruby-3.0-golang-1.15-git-2.29 test: *test_custom`
 1. Add a new build task: `ruby-3.0-golang-1.15-git-2.29 push: *build_and_deploy_custom`
 
+Note that the build name is also used for tagging the generated image, which means it cannot be
+longer than 128 characters.
+
 #### Pushing a rebuild image
 
 To build (or rebuild) a given image and push it, you need to enable manual action for a given