diff --git a/changelogs/fragments/160-dependency-collection.yml b/changelogs/fragments/160-dependency-collection.yml
new file mode 100644
index 00000000..9269f97c
--- /dev/null
+++ b/changelogs/fragments/160-dependency-collection.yml
@@ -0,0 +1,2 @@
+bugfixes:
+  - "When collecting collection dependencies for the ``lint-collection-docs`` subcommand, a bug prevented the duplicate detection to work (https://github.com/ansible-community/antsibull-docs/pull/160)."
diff --git a/src/antsibull_docs/lint_plugin_docs.py b/src/antsibull_docs/lint_plugin_docs.py
index 0389b104..d9b4adf3 100644
--- a/src/antsibull_docs/lint_plugin_docs.py
+++ b/src/antsibull_docs/lint_plugin_docs.py
@@ -602,6 +602,7 @@ def lint_collection_plugin_docs(
                 dependency = dependencies.pop(0)
                 if dependency in done_dependencies:
                     continue
+                done_dependencies.add(dependency)
                 dep_namespace, dep_name = dependency.split(".", 2)
                 dep_collection_path = collection_finder.find(dep_namespace, dep_name)
                 if dep_collection_path: