diff --git a/src/main/java/net/fortuna/ical4j/model/Component.java b/src/main/java/net/fortuna/ical4j/model/Component.java
index dc1351cf5..6186a73d5 100644
--- a/src/main/java/net/fortuna/ical4j/model/Component.java
+++ b/src/main/java/net/fortuna/ical4j/model/Component.java
@@ -190,6 +190,22 @@ public final Property getProperty(final String name) {
         return getProperties().getProperty(name);
     }
 
+    /**
+     * Convenience method for retrieving a named property.
+     *
+     * @param name name of the property to retrieve
+     * @param optional flag to indicate whether an exception should be thrown for missing property
+     * @return the first matching property in the property list with the specified name
+     * @throws ConstraintViolationException when a property is not found and the optional flag is false
+     */
+    protected final Property getProperty(String name, boolean optional) throws ConstraintViolationException {
+        Property p = getProperties().getProperty(name);
+        if (p == null && !optional) {
+            throw new ConstraintViolationException(String.format("Missing %s property", name));
+        }
+        return p;
+    }
+
     /**
      * Perform validation on a component and its properties.
      *
diff --git a/src/main/java/net/fortuna/ical4j/model/component/Observance.java b/src/main/java/net/fortuna/ical4j/model/component/Observance.java
index b952be167..c36e23274 100644
--- a/src/main/java/net/fortuna/ical4j/model/component/Observance.java
+++ b/src/main/java/net/fortuna/ical4j/model/component/Observance.java
@@ -155,10 +155,7 @@ public final Date getLatestOnset(final Date date) {
 
         if (initialOnset == null) {
             try {
-                DtStart dtStart = (DtStart) getProperty(Property.DTSTART);
-                if (dtStart == null) {
-                    throw new ConstraintViolationException("Missing DTSTART property");
-                }
+                DtStart dtStart = (DtStart) getProperty(Property.DTSTART, false);
                 initialOnset = applyOffsetFrom(calculateOnset(dtStart.getDate()));
             } catch (ParseException e) {
                 Logger log = LoggerFactory.getLogger(Observance.class);