diff --git a/core/config/schema/core.data_types.schema.yml b/core/config/schema/core.data_types.schema.yml
index 130d4cc..39f3299 100644
--- a/core/config/schema/core.data_types.schema.yml
+++ b/core/config/schema/core.data_types.schema.yml
@@ -416,9 +416,17 @@ core.date_format.*:
       type: boolean
       label: 'Locked'
     pattern:
-      type: date_format
+      type: core_date_format_pattern.[%parent.locked]
       label: 'PHP date format'
 
+core_date_format_pattern.:
+  type: date_format
+  label: 'Date format'
+
+core_date_format_pattern.1:
+  type: string
+  label: 'Date format'
+
 # Generic field settings schemas.
 
 field.storage_settings.*: