diff --git a/scripts/ShapeAlgorithms.js b/scripts/ShapeAlgorithms.js
index 7dee51db9f..c7724a1e68 100644
--- a/scripts/ShapeAlgorithms.js
+++ b/scripts/ShapeAlgorithms.js
@@ -1739,6 +1739,10 @@ ShapeAlgorithms.splineToLineOrArc = function(spline, tolerance, linesOnly) {
  * Converts the given circle into an arc with the given start angle or 0.
  */
 ShapeAlgorithms.circleToArc = function(circle, startAngle) {
+    if (isNull(startAngle)) {
+        startAngle = 0.0;
+    }
+
     return circle.toArc(startAngle);
 };