diff --git a/README.md b/README.md
index 6dad5f5..b11a4b6 100644
--- a/README.md
+++ b/README.md
@@ -109,7 +109,9 @@ Extra command to invoke before ansible-test **(OPTIONAL)**
 Whether to use change detection for pull requests. If set to `true`, will
 use change detection to determine changed files against the target branch,
 and will not upload code coverage results. If the invocation is not from a
-pull request, this option is ignored. **(DEFAULT: `false`)**
+pull request, this option is ignored. Note that this requires
+`collection-src-directory` to be empty or something ending with
+`ansible_collections/{namespace}/{name}`. **(DEFAULT: `false`)**
 
 
 ### `python-version`
diff --git a/action.yml b/action.yml
index 60c0a1d..86ae6cc 100644
--- a/action.yml
+++ b/action.yml
@@ -50,7 +50,9 @@ inputs:
       Whether to use change detection for pull requests. If set to `true`, will
       use change detection to determine changed files against the target
       branch, and will not upload code coverage results. If the invocation is
-      not from a pull request, this option is ignored.
+      not from a pull request, this option is ignored. Note that this requires
+      `collection-src-directory` to be empty or something ending with
+      `ansible_collections/{namespace}/{name}`.
     default: 'false'
   python-version:
     description: >-