diff --git a/docs/3.2.3. Input validation.md b/docs/3.2.3. Input validation.md
index 8b16743..6874692 100644
--- a/docs/3.2.3. Input validation.md	
+++ b/docs/3.2.3. Input validation.md	
@@ -9,7 +9,7 @@ We can use this for input validation, for example.
 
 ```hcl
 # stacks/owners.tf
-{% if 'owner' in var %}{{ throw('var.owner is not defined') }}{% endif %}
+{% if 'owner' not in var %}{{ throw('var.owner is not defined') }}{% endif %}
 {% if var.owner not in var.owners %}{{ throw('var.owner not in var.owners') }}{% endif %}
 ```