diff --git a/schemas/activity/cranialWindowPreparation.schema.tpl.json b/schemas/activity/cranialWindowPreparation.schema.tpl.json
index b26c1cb..da81d75 100644
--- a/schemas/activity/cranialWindowPreparation.schema.tpl.json
+++ b/schemas/activity/cranialWindowPreparation.schema.tpl.json
@@ -14,7 +14,7 @@
     "dimension": {
       "_instruction": "Enter the dimension of the cranial window by defining its mathematical shape.",
       "_embeddedCategories": [
-        "mathematicalShapes"
+        "mathematicalShape"
       ]
     },
     "input": {