diff --git a/dba/rrule_functions.sql b/dba/rrule_functions.sql
index 9aab1b31..f33731a1 100644
--- a/dba/rrule_functions.sql
+++ b/dba/rrule_functions.sql
@@ -641,13 +641,19 @@ DECLARE
   repeatrule ALIAS FOR $3;
   in_mindate ALIAS FOR $4;
   in_maxdate ALIAS FOR $5;
+  base_date TIMESTAMP WITH TIME ZONE;
   mindate TIMESTAMP WITH TIME ZONE;
   maxdate TIMESTAMP WITH TIME ZONE;
 BEGIN
 
-  IF dtstart IS NULL OR dtend IS NULL THEN
+  IF dtstart IS NULL THEN
     RETURN NULL;
   END IF;
+  IF dtend IS NULL THEN
+    base_date := dtstart;
+  ELSE
+    base_date := dtend;
+  END IF;
 
   IF in_mindate IS NULL THEN
     mindate := current_date - '10 years'::interval;
@@ -659,14 +665,14 @@ BEGIN
     maxdate := current_date + '10 years'::interval;
   ELSE
     -- If we add the duration onto the event, then an overlap occurs if dtend <= increased end of range.
-    maxdate := in_maxdate + (dtend - dtstart);
+    maxdate := in_maxdate + (base_date - dtstart);
   END IF;
 
   IF repeatrule IS NULL THEN
-    RETURN (dtstart <= maxdate AND dtend >= mindate);
+    RETURN (dtstart <= maxdate AND base_date >= mindate);
   END IF;
 
-  SELECT d INTO mindate FROM rrule_event_instances_range( dtend, repeatrule, mindate, maxdate, 3 ) d LIMIT 1;
+  SELECT d INTO mindate FROM rrule_event_instances_range( base_date, repeatrule, mindate, maxdate, 60 ) d LIMIT 1;
   RETURN FOUND;
 
 END;