diff --git a/prism/src/chart/GraphPoint.java b/prism/src/chart/GraphPoint.java
index 33c165e0..1525293e 100644
--- a/prism/src/chart/GraphPoint.java
+++ b/prism/src/chart/GraphPoint.java
@@ -1,6 +1,6 @@
 //==============================================================================
 //	
-//	Copyright (c) 2002-2004, Andrew Hinton
+//	Copyright (c) 2002-2006 Andrew Hinton, Dave Parker
 //	
 //	This file is part of PRISM.
 //	
@@ -84,6 +84,22 @@ public class GraphPoint
 		//theModel.workOutAndSetYScales();
     }
     
+	// Check that point is valid (x/y not +/- infnity or NaN)
+	
+	public boolean isValid()
+	{
+		// x = +/- infinity
+		if (xCoord == Double.POSITIVE_INFINITY || xCoord == Double.NEGATIVE_INFINITY) return false;
+		// x = NaN
+		if (xCoord != xCoord) return false;
+		// y = +/- infinity
+		if (yCoord == Double.POSITIVE_INFINITY || yCoord == Double.NEGATIVE_INFINITY) return false;
+		// y = NaN
+		if (yCoord != yCoord) return false;
+		// valid
+		return true;
+	}
+	
     /** Returns a string describing this point.  This method is used to generate the
      * tooltips.
      */    
diff --git a/prism/src/chart/MultiGraphModel.java b/prism/src/chart/MultiGraphModel.java
index 441bcb2e..67c645a5 100644
--- a/prism/src/chart/MultiGraphModel.java
+++ b/prism/src/chart/MultiGraphModel.java
@@ -1,6 +1,6 @@
 //==============================================================================
 //
-//	Copyright (c) 2002-2005, Andrew Hinton
+//	Copyright (c) 2002-2006, Andrew Hinton, Dave Parker
 //
 //	This file is part of PRISM.
 //
@@ -1028,6 +1028,9 @@ public class MultiGraphModel extends Observable implements SettingOwner, ListMod
 	 */
 	public synchronized void addPoint(int graphIndex, GraphPoint p, boolean sortAfter, boolean autoX, boolean autoY) throws SettingException
 	{
+		// Check point valid (no infinity/NaN)
+		if (!p.isValid()) return;
+		
 		((GraphList)graphs.get(graphIndex)).add(p);
 		if(sortAfter)((GraphList)graphs.get(graphIndex)).sortPoints(sortBy);
 		
diff --git a/prism/src/prism/DisplayableData.java b/prism/src/prism/DisplayableData.java
index e01e2d11..1ac6a26b 100644
--- a/prism/src/prism/DisplayableData.java
+++ b/prism/src/prism/DisplayableData.java
@@ -68,13 +68,11 @@ public class DisplayableData
 	
 	public void notifyResult(Values v, Object result)
 	{
-		//System.out.println("**********************************************");
-		//System.out.println("notifying result "+v+" = "+result);
 		Object obj = shouldAddThis(v);
 		if(obj != null)
 		{
-			//System.out.println("this should be added");
 			double x,y;
+			// Get x coordinate
 			if(obj instanceof Integer)
 			{
 				x = ((Integer)obj).intValue();
@@ -83,7 +81,11 @@ public class DisplayableData
 			{
 				x = ((Double)obj).doubleValue();
 			}
+			// Cancel if non integer/double
 			else return;
+			// Cancel if +/- infinity or NaN
+			if (x == Double.POSITIVE_INFINITY || x == Double.NEGATIVE_INFINITY || x != x) return;
+			// Get y coordinate
 			if(result instanceof Integer)
 			{
 				y = ((Integer)result).intValue();
@@ -92,7 +94,11 @@ public class DisplayableData
 			{
 				y = ((Double)result).doubleValue();
 			}
+			// Cancel if non integer/double
 			else return;
+			// Cancel if +/- infinity or NaN
+			if (y == Double.POSITIVE_INFINITY || y == Double.NEGATIVE_INFINITY || y != y) return;
+			// Add point to graph
 			try
 			{
 				GraphPoint existing = getExistingGraphPoint(v);
@@ -115,10 +121,6 @@ public class DisplayableData
 				//do nothing
 			}
 		}
-		else
-		{
-			//System.out.println("should not be added");
-		}
 	}
 	
 	public void clear()
@@ -154,7 +156,6 @@ public class DisplayableData
 	 *	the value of the rangeConstant.  If not this returns null. */
 	public Object shouldAddThis(Values v)
 	{
-		boolean shouldAdd = true;
 		for(int i = 0; i < otherValues.getNumValues(); i++)
 		{
 			String name = otherValues.getName(i);