diff --git a/src/meshbuilder.cpp b/src/meshbuilder.cpp
index 66c8afc..da3f52e 100644
--- a/src/meshbuilder.cpp
+++ b/src/meshbuilder.cpp
@@ -125,13 +125,13 @@ void MeshBuilder::mergeVertices()
     std::set<int, VertexComparator> vertexSet;
     VertexComparator::setMesh(this);
 
-    int size = positions.size();
+    int swappedOffset = positions.size() - 1;
 
     for(Group &g : indiceGroups)
     for(int i=0; i<g.indices.size(); ++i)
     {
         if(g.indices[i] >= positions.size())
-            g.indices[i] = swapped[size - g.indices[i]];
+            g.indices[i] = swapped[swappedOffset - g.indices[i]];
         std::pair<std::set<int,VertexComparator>::iterator,bool> ret = vertexSet.insert(g.indices[i]);
         if(!ret.second) // duplicate found
         {
@@ -154,13 +154,18 @@ void MeshBuilder::mergeVertices()
             }
             if(hasTangents())
             {
+                tangents[g.indices[i]].tangent += tangents[toDelete].tangent;
+                tangents[g.indices[i]].binormal += tangents[toDelete].binormal;
                 tangents[toDelete] = tangents.back();
                 tangents.pop_back();
             }
         }
     }
-
-    fprintf(stdout, "found %d vertex duplicates\n", swapped.size());
+    for(Tangents &t : tangents)
+    {
+        t.tangent = glm::normalize(t.tangent);
+        t.binormal = glm::normalize(t.binormal);
+    }
 }
 
 void MeshBuilder::computeNormals()