diff --git a/Grapher/src/graph/LineGraph.java b/Grapher/src/graph/LineGraph.java
index 6df6137..e55c08e 100644
--- a/Grapher/src/graph/LineGraph.java
+++ b/Grapher/src/graph/LineGraph.java
@@ -176,6 +176,10 @@ public void addValue(double value){
      * @param point using cartesian coordinates.
      */
     public void addPoint(Point2D point){
+        if(point.getX() == Double.NaN)
+            throw new RuntimeException("X value must be a number.");
+        if(point.getY() == Double.NaN)
+            throw new RuntimeException();
         point = translate(point);
         points.add(point);
         isNormalized = false;