diff --git a/docker-compose.yml b/docker-compose.yml
index 27109dc..a7c4c2d 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -109,6 +109,7 @@ services:
       DB_USER: ${POSTGRES_USER:-prod_user}
       DB_PASSWORD: ${POSTGRES_PASSWORD:?POSTGRES_PASSWORD is required}
       SYNC_HTTP_PORT: 3001
+      FDISK_DEBUG_HTML: ${FDISK_DEBUG_HTML:-}
     depends_on:
       postgres:
         condition: service_healthy
diff --git a/frontend/src/pages/Kalender.tsx b/frontend/src/pages/Kalender.tsx
index 3298279..4ee8296 100644
--- a/frontend/src/pages/Kalender.tsx
+++ b/frontend/src/pages/Kalender.tsx
@@ -1519,10 +1519,11 @@ function VeranstaltungFormDialog({
             onChange={(e) => {
               const raw = e.target.value;
               if (!raw) return;
-              const iso = form.ganztaegig
-                ? new Date(raw + 'T00:00:00').toISOString()
-                : new Date(raw).toISOString();
-              handleChange('datum_von', iso);
+              const d = form.ganztaegig
+                ? new Date(raw + 'T00:00:00')
+                : new Date(raw + ':00');
+              if (isNaN(d.getTime())) return;
+              handleChange('datum_von', d.toISOString());
             }}
             InputLabelProps={{ shrink: true }}
             fullWidth
@@ -1538,9 +1539,12 @@ function VeranstaltungFormDialog({
             onChange={(e) => {
               const raw = e.target.value;
               if (!raw) return;
-              const iso = form.ganztaegig
-                ? new Date(raw + 'T23:59:00').toISOString()
-                : new Date(raw).toISOString();
+              const d = form.ganztaegig
+                ? new Date(raw + 'T23:59:00')
+                : new Date(raw + ':00');
+              if (isNaN(d.getTime())) return;
+              handleChange('datum_bis', d.toISOString());
+            }}
               handleChange('datum_bis', iso);
             }}
             InputLabelProps={{ shrink: true }}