diff --git a/docs/yaml/functions/subdir.yaml b/docs/yaml/functions/subdir.yaml
index 694fa518f..428563b37 100644
--- a/docs/yaml/functions/subdir.yaml
+++ b/docs/yaml/functions/subdir.yaml
@@ -14,7 +14,10 @@ description: |
 posargs:
   dir_name:
     type: str
-    description: Directory relative to the current `meson.build` to enter.
+    description: |
+      Directory relative to the current `meson.build` to enter.
+
+      Cannot contain `..`
 
 kwargs:
   if_found: