diff --git a/lib/path-set.js b/lib/path-set.js
index 9ba52af..eb0cda5 100644
--- a/lib/path-set.js
+++ b/lib/path-set.js
@@ -31,15 +31,14 @@ class PathSet {
 
 
   add(path) {
-    var sets = [];
+    let sets;
 
-    if (!this.lengthIndex[path.length]) {
-      sets = null;
+    if (!this.lengthIndex[path.length])
       this.lengthIndex[path.length] = new Set();
-    }
-    else if (sets) {
-      sets.push(this.lengthIndex[path.length])
-    }
+    else if (this.lengthIndex[path.length].has(path))
+      return path;
+    else
+      sets = [this.lengthIndex[path.length]];
 
     for (let i = 0; i < path.length; ++ i) {
       let fragment = path[i];
@@ -53,7 +52,7 @@ class PathSet {
       }
 
       if (!this.fragmentIndex[i][fragment]) {
-        sets = null
+        sets = null;
         this.fragmentIndex[i][fragment] = new Set();
       }
       else if (sets)