diff --git a/prism/src/parser/PrismParser.jj b/prism/src/parser/PrismParser.jj
index bcfee6d3..68188d93 100644
--- a/prism/src/parser/PrismParser.jj
+++ b/prism/src/parser/PrismParser.jj
@@ -1350,16 +1350,16 @@ AccumulationFunction ExpressionAccumulationFunction() :
 }
 {
 	(  (LOOKAHEAD({ getToken(1).kind==REG_IDENT && getToken(1).image.equals("time") })
-	   Identifier() {func = AccumulationFunction.ACC_TIME;})
+	   Identifier() {func = new AccumulationFunction(AccumulationType.ACC_TIME);})
 	 | (LOOKAHEAD({ getToken(1).kind==REG_IDENT && getToken(1).image.equals("steps") })
-	   Identifier() {func = AccumulationFunction.ACC_STEPS;})
+	   Identifier() {func = new AccumulationFunction(AccumulationType.ACC_STEPS);})
 
 	   // SWDO: We also want "weight" here
  	 | (LOOKAHEAD({ getToken(1).kind==REG_IDENT && getToken(1).image.equals("reward") })
 	   Identifier()
  		 (rewardIndex = RewardIndex())?
  		 {
-		   func = AccumulationFunction.ACC_REWARD;
+		   func = new AccumulationFunction(AccumulationType.ACC_REWARD);
 		   func.setRewardIndex(rewardIndex);
  		 })
 	)
diff --git a/prism/src/parser/ast/AccumulationFunction.java b/prism/src/parser/ast/AccumulationFunction.java
index 53b839a4..209758ae 100644
--- a/prism/src/parser/ast/AccumulationFunction.java
+++ b/prism/src/parser/ast/AccumulationFunction.java
@@ -1,7 +1,11 @@
 package parser.ast;
 
-public enum AccumulationFunction {
-	ACC_TIME, ACC_STEPS, ACC_REWARD;
+public class AccumulationFunction {
+	public AccumulationFunction(AccumulationType type) {
+		this.type = type;
+	}
+	
+	public AccumulationType type;
 	
 	private Object rewardIndex = null;
 	
@@ -14,7 +18,7 @@ public enum AccumulationFunction {
 	}
 	
 	public String toString() {
-		switch(this) {
+		switch(this.type) {
 		case ACC_REWARD:
 			return "reward" + indexString();
 		case ACC_STEPS:
diff --git a/prism/src/parser/ast/AccumulationType.java b/prism/src/parser/ast/AccumulationType.java
new file mode 100644
index 00000000..d7822cbc
--- /dev/null
+++ b/prism/src/parser/ast/AccumulationType.java
@@ -0,0 +1,5 @@
+package parser.ast;
+
+public enum AccumulationType {
+	ACC_TIME, ACC_STEPS, ACC_REWARD;
+}