diff --git a/OpenKh.Command.MapGen/Utils/FlattenCollisionBuilder.cs b/OpenKh.Command.MapGen/Utils/FlattenCollisionBuilder.cs
index 42a0f5b19..a3d6a1ffa 100644
--- a/OpenKh.Command.MapGen/Utils/FlattenCollisionBuilder.cs
+++ b/OpenKh.Command.MapGen/Utils/FlattenCollisionBuilder.cs
@@ -56,7 +56,7 @@ Func<MaterialDef, int> getAttributeFrom
                         var v3 = face.positionList[2];
                         var v4 = quad ? face.positionList[3] : Vector3.Zero;
 
-                        collisionMesh.Collisions.Add(coct.Complete(
+                        var collision = coct.Complete(
                             new Collision
                             {
                                 Vertex1 = helper.AllocateVertex(v1.X, -v1.Y, -v1.Z), // why -Y and -Z ?
@@ -68,7 +68,16 @@ Func<MaterialDef, int> getAttributeFrom
                                 FloorLevel = face.matDef.floorLevel,
                             },
                             inflate: 1
-                        ));
+                        );
+
+                        if (float.IsNaN(collision.Plane.D))
+                        {
+                            // 3 points are on the same line (not a plane)
+                        }
+                        else
+                        {
+                            collisionMesh.Collisions.Add(collision);
+                        }
                     }
 
                     if (collisionMesh.Collisions.Any())
diff --git a/OpenKh.Command.MapGen/Utils/HierarchicalCollisionBuilder.cs b/OpenKh.Command.MapGen/Utils/HierarchicalCollisionBuilder.cs
index f950beb6b..02feadcbc 100644
--- a/OpenKh.Command.MapGen/Utils/HierarchicalCollisionBuilder.cs
+++ b/OpenKh.Command.MapGen/Utils/HierarchicalCollisionBuilder.cs
@@ -70,7 +70,7 @@ private WalkResult WalkTree(Node walkNode, BuildHelper helper)
                     var v3 = face.positionList[2];
                     var v4 = quad ? face.positionList[3] : Vector3.Zero;
 
-                    collisionMesh.Collisions.Add(coct.Complete(
+                    var collision = coct.Complete(
                         new Collision
                         {
                             Vertex1 = helper.AllocateVertex(v1.X, -v1.Y, -v1.Z), // why -Y and -Z ?
@@ -82,7 +82,16 @@ private WalkResult WalkTree(Node walkNode, BuildHelper helper)
                             FloorLevel = face.matDef.floorLevel,
                         },
                         inflate: 1
-                    ));
+                    );
+
+                    if (float.IsNaN(collision.Plane.D))
+                    {
+                        // 3 points are on the same line (not a plane)
+                    }
+                    else
+                    {
+                        collisionMesh.Collisions.Add(collision);
+                    }
                 }
 
                 coct.Complete(collisionMesh);