diff --git a/model.py b/model.py
index ecd9039..480ee13 100644
--- a/model.py
+++ b/model.py
@@ -28,6 +28,9 @@ def get_cycle_position(date, halving_dates):
     Calculate position in halving cycle (0 to 1) for a given date.
     0 represents a halving event, 1 represents just before the next halving.
     """
+    if len(halving_dates) == 0:
+        raise Exception("halving dates cannot be empty")
+
     # Convert date to datetime if it's not already
     date = pd.to_datetime(date)