diff --git a/package_linter.py b/package_linter.py
index 281684a..6e25c7e 100755
--- a/package_linter.py
+++ b/package_linter.py
@@ -1967,6 +1967,9 @@ class Manifest(TestSuite):
 
                 apt_packages = resources["apt"].get("packages", [])
                 if isinstance(apt_packages, str):
+                    yield Warning(
+                        "The packages list should be a TOML list, like [ 'package1', 'package2' ]. Using a string separated with commas/spaces will be deprecated in the future."
+                    )
                     apt_packages = [value.strip() for value in re.split(' |,',apt_packages)]
 
                 if dbtype == "mysql" and "mariadb-server" not in apt_packages: