diff --git a/frontend/src/lib/components/StringTypeNarrowing.svelte b/frontend/src/lib/components/StringTypeNarrowing.svelte
index b960653b64..ae9b4e9a9d 100644
--- a/frontend/src/lib/components/StringTypeNarrowing.svelte
+++ b/frontend/src/lib/components/StringTypeNarrowing.svelte
@@ -120,6 +120,8 @@
 				}
 				if (e.detail == 'date-time') {
 					format = 'date-time'
+				} else if (format) {
+					format = undefined
 				}
 				if (e.detail == 'none') {
 					pattern = undefined