diff --git a/doc/09-object-types.md b/doc/09-object-types.md
index b1273516c..8b6edf34d 100644
--- a/doc/09-object-types.md
+++ b/doc/09-object-types.md
@@ -1486,6 +1486,11 @@ Cleanup Items:
   servicechecks\_age              | Duration              | **Optional.** Max age for servicechecks table rows (start\_time). Defaults to 0 (never).
   systemcommands\_age             | Duration              | **Optional.** Max age for systemcommands table rows (start\_time). Defaults to 0 (never).
 
+> **Supported units**
+>
+> Supported suffixes include ms (milliseconds), s (seconds), m (minutes), h (hours) and d (days).
+> Check the [language reference](17-language-reference.md#duration-literals).
+
 Data Categories:
 
   Name                 | Description            | Required by
@@ -1580,6 +1585,11 @@ Cleanup Items:
   servicechecks\_age              | Duration              | **Optional.** Max age for servicechecks table rows (start\_time). Defaults to 0 (never).
   systemcommands\_age             | Duration              | **Optional.** Max age for systemcommands table rows (start\_time). Defaults to 0 (never).
 
+> **Supported units**
+>
+> Supported suffixes include ms (milliseconds), s (seconds), m (minutes), h (hours) and d (days).
+> Check the [language reference](17-language-reference.md#duration-literals).
+
 Data Categories:
 
   Name                 | Description            | Required by