diff --git a/Scripts/demand/trips.py b/Scripts/demand/trips.py
index dab28ed1..da825f62 100644
--- a/Scripts/demand/trips.py
+++ b/Scripts/demand/trips.py
@@ -110,20 +110,16 @@ def create_population(self):
         # Group -1 is under-7-year-olds
         age_range = numpy.arange(-1, len(param.age_groups))
         for zone_number in zone_numbers:
-            weights = [self.zone_data[f"share_{age}"][zone_number]
-                for age in self._age_strings()]
+            weights = numpy.array([self.zone_data[f"share_{age}"][zone_number]
+                for age in self._age_strings()])
             # Append under-7 weight
-            weights = [max(1 - sum(weights), 0)] + weights
-            if sum(weights) > 1:
-                if sum(weights) > 1.005:
-                    msg = "Sum of age group shares for zone {} is {}".format(
-                        zone_number, sum(weights))
-                    log.error(msg)
-                    raise ValueError(msg)
-                else:
-                    weights = numpy.array(weights)
-                    rebalance = 1 / sum(weights)
-                    weights = rebalance * weights
+            weights = numpy.insert(weights, 0, max(1.0 - weights.sum(), 0.0))
+            if sum(weights) > 1.005:
+                msg = "Sum of age group shares for zone {} is {}".format(
+                    zone_number, sum(weights))
+                log.error(msg)
+                raise ValueError(msg)
+            weights *= 1.0/weights.sum() # Normalize weights
             zone_pop = int(round(self.zone_data["population"][zone_number]
                                  * param.agent_demand_fraction))
             zone = self.zone_data.zones[zone_number]