diff --git a/Geometry_Engine/Query/IsClosed.cs b/Geometry_Engine/Query/IsClosed.cs
index bd563c772..c6d11c99c 100644
--- a/Geometry_Engine/Query/IsClosed.cs
+++ b/Geometry_Engine/Query/IsClosed.cs
@@ -67,8 +67,7 @@ public static bool IsClosed(this NurbsCurve curve, double tolerance = Tolerance.
             if (curve == null || curve.ControlPoints == null || curve.ControlPoints.Count < 2)
                 return false;
 
-            // TODO: This does not take into account periodic curves
-            return curve.ControlPoints.First() == curve.ControlPoints.Last();
+            return curve.ControlPoints.First().SquareDistance(curve.ControlPoints.Last()) <= tolerance * tolerance || curve.IsPeriodic();
         }
 
         /***************************************************/
diff --git a/Geometry_Engine/Query/IsPeriodic.cs b/Geometry_Engine/Query/IsPeriodic.cs
index 81e36017f..c574d1401 100644
--- a/Geometry_Engine/Query/IsPeriodic.cs
+++ b/Geometry_Engine/Query/IsPeriodic.cs
@@ -31,6 +31,18 @@ public static partial class Query
         /**** Public Methods                            ****/
         /***************************************************/
 
+        public static bool IsPeriodic(this NurbsCurve curve)
+        {
+            int multiplicity = 1;
+
+            while (curve.Knots[multiplicity - 1] == curve.Knots[multiplicity])
+                multiplicity++;
+
+            return (multiplicity != curve.Degree());
+        }
+
+        /***************************************************/
+        
         public static bool IsPeriodic(this NurbsSurface surface)
         {
             int uMultiplicity = 1;