diff --git a/core/src/net/sf/openrocket/simulation/customexpression/CustomExpression.java b/core/src/net/sf/openrocket/simulation/customexpression/CustomExpression.java
index 7102b55be..e233deff9 100644
--- a/core/src/net/sf/openrocket/simulation/customexpression/CustomExpression.java
+++ b/core/src/net/sf/openrocket/simulation/customexpression/CustomExpression.java
@@ -352,7 +352,9 @@ public class CustomExpression implements Cloneable{
 	}
 	
 	public Double evaluateDouble(SimulationStatus status){
-		return evaluate(status).getDoubleValue();
+		double result = evaluate(status).getDoubleValue();
+		if (result == Double.NEGATIVE_INFINITY || result == Double.POSITIVE_INFINITY) result = Double.NaN;
+		return result;
 	}
 	
 	/*
@@ -498,9 +500,10 @@ public class CustomExpression implements Cloneable{
 	 * Used for temporary substitution when evaluating index and range expressions.
 	 */
 	public String hash(){
-		Integer hashint = new Integer(this.getExpressionString().hashCode());
+		Integer hashint = new Integer(this.getExpressionString().hashCode() + symbol.hashCode());
 		String hash = "$";
 		for (char c : hashint.toString().toCharArray()){
+			if (c == '-') c = '0';
 			char newc = (char) (c + 17);
 			hash = hash + newc;
 		}