diff --git a/lib/spira.rb b/lib/spira.rb
index 3fa2e2c..1277dc7 100644
--- a/lib/spira.rb
+++ b/lib/spira.rb
@@ -3,6 +3,7 @@
 require "promise"
 require "spira/exceptions"
 require "spira/utils"
+require "rdf/vocab"
 
 ##
 # Spira is a framework for building projections of RDF data into Ruby classes.