diff --git a/src/pytest_dependency.py b/src/pytest_dependency.py
index 43224ee..26b6585 100644
--- a/src/pytest_dependency.py
+++ b/src/pytest_dependency.py
@@ -89,7 +89,7 @@ def checkDepend(self, depends, item):
                 else:
                     logger.debug("... %s has not succeeded", i)
             else:
-                logger.debug("... %s is unknown", i)
+                logger.debug("... %s is unknown (did you forget to mark it?)", i)
                 if _ignore_unknown:
                     continue
             logger.info("skip %s because it depends on %s", item.name, i)