diff --git a/lib/vobject/vcalendar/propertyvalue.rb b/lib/vobject/vcalendar/propertyvalue.rb
index d455952..2c1a589 100644
--- a/lib/vobject/vcalendar/propertyvalue.rb
+++ b/lib/vobject/vcalendar/propertyvalue.rb
@@ -342,6 +342,10 @@ def to_s
         def to_hash
           value
         end
+
+        def to_norm
+          value.to_s.upcase
+        end
       end
 
       class Duration < Vobject::PropertyValue
diff --git a/spec/examples/vcalendar/boolean1.norm.ics b/spec/examples/vcalendar/boolean1.norm.ics
index c5cb332..c58b4cb 100644
--- a/spec/examples/vcalendar/boolean1.norm.ics
+++ b/spec/examples/vcalendar/boolean1.norm.ics
@@ -12,7 +12,7 @@ SEQUENCE:2
 STATUS:NEEDS-ACTION
 SUMMARY:Submit Income Taxes
 UID:uid4@example.com
-X-FALSE;VALUE="BOOLEAN":false
-X-TRUE;VALUE="BOOLEAN":true
+X-FALSE;VALUE="BOOLEAN":FALSE
+X-TRUE;VALUE="BOOLEAN":TRUE
 END:VTODO
 END:VCALENDAR