diff --git a/Triangle.NET/Triangle/Mesh.cs b/Triangle.NET/Triangle/Mesh.cs
index 9b3b21f..17f4dad 100644
--- a/Triangle.NET/Triangle/Mesh.cs
+++ b/Triangle.NET/Triangle/Mesh.cs
@@ -586,7 +586,7 @@ namespace TriangleNet
         /// Read the vertices from memory.
         /// </summary>
         /// <param name="data">The input data.</param>
-        internal void TransferNodes(ICollection<Vertex> points)
+        internal void TransferNodes(IList<Vertex> points)
         {
             this.invertices = points.Count;
             this.mesh_dim = 2;
@@ -598,17 +598,29 @@ namespace TriangleNet
                 throw new Exception("Input must have at least three input vertices.");
             }
 
-            bool first = true;
+            var v = points[0];
 
-            foreach (Vertex p in points)
+            // Check attributes.
+            this.nextras = v.attributes == null ? 0 : v.attributes.Length;
+
+            // Simple heuristic to check if ids are already set.  We assume that if the
+            // first two vertex ids are distinct, then all input vertices have pairwise
+            // distinct ids.
+            bool userId = (v.ID != points[1].ID);
+
+            foreach (var p in points)
             {
-                if (first)
+                if (userId)
                 {
-                    this.nextras = p.attributes == null ? 0 : p.attributes.Length;
-                    first = false;
-                }
+                    p.hash = p.id;
 
-                p.hash = p.id = this.hash_vtx++;
+                    // Make sure the hash counter gets updated.
+                    hash_vtx = Math.Max(p.hash, hash_vtx);
+                }
+                else
+                {
+                    p.hash = p.id = hash_vtx++;
+                }
 
                 this.vertices.Add(p.hash, p);
                 this.bounds.Expand(p);
diff --git a/Triangle.NET/Triangle/Meshing/Algorithm/Dwyer.cs b/Triangle.NET/Triangle/Meshing/Algorithm/Dwyer.cs
index 91905ea..35cb035 100644
--- a/Triangle.NET/Triangle/Meshing/Algorithm/Dwyer.cs
+++ b/Triangle.NET/Triangle/Meshing/Algorithm/Dwyer.cs
@@ -60,7 +60,7 @@ namespace TriangleNet.Meshing.Algorithm
         /// Sorts the vertices, calls a recursive procedure to triangulate them, and
         /// removes the bounding box, setting boundary markers as appropriate.
         /// </remarks>
-        public IMesh Triangulate(ICollection<Vertex> points)
+        public IMesh Triangulate(IList<Vertex> points)
         {
             this.mesh = new Mesh();
             this.mesh.TransferNodes(points);
diff --git a/Triangle.NET/Triangle/Meshing/Algorithm/Incremental.cs b/Triangle.NET/Triangle/Meshing/Algorithm/Incremental.cs
index 7fd40f9..abf73ab 100644
--- a/Triangle.NET/Triangle/Meshing/Algorithm/Incremental.cs
+++ b/Triangle.NET/Triangle/Meshing/Algorithm/Incremental.cs
@@ -23,7 +23,7 @@ namespace TriangleNet.Meshing.Algorithm
         /// </summary>
         /// <returns>Returns the number of edges on the convex hull of the 
         /// triangulation.</returns>
-        public IMesh Triangulate(ICollection<Vertex> points)
+        public IMesh Triangulate(IList<Vertex> points)
         {
             this.mesh = new Mesh();
             this.mesh.TransferNodes(points);
diff --git a/Triangle.NET/Triangle/Meshing/Algorithm/SweepLine.cs b/Triangle.NET/Triangle/Meshing/Algorithm/SweepLine.cs
index 97175fc..b53fd19 100644
--- a/Triangle.NET/Triangle/Meshing/Algorithm/SweepLine.cs
+++ b/Triangle.NET/Triangle/Meshing/Algorithm/SweepLine.cs
@@ -31,7 +31,7 @@ namespace TriangleNet.Meshing.Algorithm
         double xminextreme; // Nonexistent x value used as a flag in sweepline.
         List<SplayNode> splaynodes;
 
-        public IMesh Triangulate(ICollection<Vertex> points)
+        public IMesh Triangulate(IList<Vertex> points)
         {
             this.mesh = new Mesh();
             this.mesh.TransferNodes(points);
diff --git a/Triangle.NET/Triangle/Meshing/GenericMesher.cs b/Triangle.NET/Triangle/Meshing/GenericMesher.cs
index 12a8fa6..d0eca4d 100644
--- a/Triangle.NET/Triangle/Meshing/GenericMesher.cs
+++ b/Triangle.NET/Triangle/Meshing/GenericMesher.cs
@@ -25,7 +25,7 @@ namespace TriangleNet.Meshing
         }
 
         /// <inherit />
-        public IMesh Triangulate(ICollection<Vertex> points)
+        public IMesh Triangulate(IList<Vertex> points)
         {
             return triangulator.Triangulate(points);
         }
diff --git a/Triangle.NET/Triangle/Meshing/ITriangulator.cs b/Triangle.NET/Triangle/Meshing/ITriangulator.cs
index ea631c8..a8139bd 100644
--- a/Triangle.NET/Triangle/Meshing/ITriangulator.cs
+++ b/Triangle.NET/Triangle/Meshing/ITriangulator.cs
@@ -19,6 +19,6 @@ namespace TriangleNet.Meshing
         /// </summary>
         /// <param name="points">Collection of points.</param>
         /// <returns>Mesh</returns>
-        IMesh Triangulate(ICollection<Vertex> points);
+        IMesh Triangulate(IList<Vertex> points);
     }
 }