Index: openacs-4/packages/calendar/tcl/cal-item-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/calendar/tcl/cal-item-procs.tcl,v
diff -u -N -r1.35.2.6 -r1.35.2.7
--- openacs-4/packages/calendar/tcl/cal-item-procs.tcl	19 Feb 2021 09:47:12 -0000	1.35.2.6
+++ openacs-4/packages/calendar/tcl/cal-item-procs.tcl	25 Jan 2022 14:00:42 -0000	1.35.2.7
@@ -21,7 +21,20 @@
 } {
     A sanity check that the start time is before the end time.
 } {
-    return [db_string dates_valid_p_select {}]
+    try {
+        return [db_string dates_valid_p_select {
+            select CASE
+              WHEN cast(:start_date as timestamp with time zone)
+                   <=
+                   cast(:end_date as timestamp with time zone) THEN 1
+              ELSE 0
+            END from dual
+        }]
+    } on error {errmsg} {
+        # Invalid dates in input, definitely not ok.
+        ad_log warning $errmsg
+        return 0
+    }
 }
 
 ad_proc -public calendar::item::new {