diff --git a/src/main/java/org/opentripplanner/ojp/time/XmlDateTime.java b/src/main/java/org/opentripplanner/ojp/time/XmlDateTime.java
index eff695f..7a0f7b9 100644
--- a/src/main/java/org/opentripplanner/ojp/time/XmlDateTime.java
+++ b/src/main/java/org/opentripplanner/ojp/time/XmlDateTime.java
@@ -4,6 +4,7 @@
 import java.time.ZoneId;
 import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
+import java.time.temporal.ChronoUnit;
 import java.util.Objects;
 
 /**
@@ -23,6 +24,13 @@ public XmlDateTime(LocalDateTime localDateTime) {
     this.localDateTime = Objects.requireNonNull(localDateTime);
   }
 
+  /**
+   * Return a truncated version of the given date time with millisecond precision.
+   */
+  public static XmlDateTime truncatedToMillis(ZonedDateTime dateTime) {
+    return new XmlDateTime(dateTime.truncatedTo(ChronoUnit.MILLIS));
+  }
+
   /**
    * Converts the abstract XML dateTime into a {@link ZonedDateTime}. If the underlying date time
    * was already zoned, then it is converted to the same instant but in the specified zone.