diff --git a/core/models/survex.py b/core/models/survex.py
index f62d93b..7b69b64 100644
--- a/core/models/survex.py
+++ b/core/models/survex.py
@@ -229,7 +229,11 @@ class SurvexBlock(models.Model):
         """This is used to set different colours for the different trips on
         the calendar view of the expedition"""
         mx = 10
-        index = list(SurvexBlock.objects.filter(date=self.date)).index(self)
+        try:
+            index = list(SurvexBlock.objects.filter(date=self.date)).index(self)
+        except:
+            print(f"DayIndex: BAD BAD BAD SurvexBlock items on one day '{index}' {self}")
+            index = 0
         if index not in range(0, mx):
             print(f"DayIndex: More than {mx-1} SurvexBlock items on one day '{index}' {self}")
             index = 0