diff --git a/src/main/java/org/umlgraph/doclet/ClassGraph.java b/src/main/java/org/umlgraph/doclet/ClassGraph.java
index b399934..7d3d557 100644
--- a/src/main/java/org/umlgraph/doclet/ClassGraph.java
+++ b/src/main/java/org/umlgraph/doclet/ClassGraph.java
@@ -623,7 +623,7 @@ class ClassGraph {
      * @param edgetype the dot edge specification
      */
     private void allRelation(Options opt, RelationType rt, ClassDoc from) {
-	String tagname = rt.toString().toLowerCase();
+	String tagname = rt.lower;
 	for (Tag tag : from.tags(tagname)) {
 	    String t[] = StringUtil.tokenize(tag.text());    // l-src label l-dst target
 	    if (t.length != 4) {
diff --git a/src/main/java/org/umlgraph/doclet/RelationType.java b/src/main/java/org/umlgraph/doclet/RelationType.java
index eb6b4cf..ba4eeb5 100644
--- a/src/main/java/org/umlgraph/doclet/RelationType.java
+++ b/src/main/java/org/umlgraph/doclet/RelationType.java
@@ -6,5 +6,11 @@ package org.umlgraph.doclet;
  * 
  */
 public enum RelationType {
-    ASSOC, NAVASSOC, HAS, NAVHAS, COMPOSED, NAVCOMPOSED, DEPEND, EXTENDS, IMPLEMENTS;
+    ASSOC(), NAVASSOC(), HAS(), NAVHAS(), COMPOSED(), NAVCOMPOSED(), DEPEND(), EXTENDS(), IMPLEMENTS();
+
+    public final String lower;
+
+    private RelationType() {
+        this.lower = toString().toLowerCase();
+    }
 }