diff --git a/prism/src/explicit/DTMCModelChecker.java b/prism/src/explicit/DTMCModelChecker.java
index 7e33180c..d689a759 100644
--- a/prism/src/explicit/DTMCModelChecker.java
+++ b/prism/src/explicit/DTMCModelChecker.java
@@ -1345,6 +1345,11 @@ public class DTMCModelChecker extends ProbModelChecker
 	 */
 	double computeReachRewardsUpperBound(DTMC dtmc, MCRewards mcRewards, BitSet target, BitSet unknown, BitSet inf) throws PrismException
 	{
+		if (unknown.isEmpty()) {
+			mainLog.println("Skipping upper bound computation, no unknown states...");
+			return 0;
+		}
+
 		// inf and target states become trap states (with self-loops)
 		BitSet trapStates = (BitSet) target.clone();
 		trapStates.or(inf);
diff --git a/prism/src/explicit/MDPModelChecker.java b/prism/src/explicit/MDPModelChecker.java
index 5f4696b1..8b01a24f 100644
--- a/prism/src/explicit/MDPModelChecker.java
+++ b/prism/src/explicit/MDPModelChecker.java
@@ -1414,6 +1414,11 @@ public class MDPModelChecker extends ProbModelChecker
 	 */
 	double computeReachRewardsMaxUpperBound(MDP mdp, MDPRewards mdpRewards, BitSet target, BitSet unknown, BitSet inf) throws PrismException
 	{
+		if (unknown.isEmpty()) {
+			mainLog.println("Skipping upper bound computation, no unknown states...");
+			return 0;
+		}
+
 		// inf and target states become trap states (with dropped choices)
 		BitSet trapStates = (BitSet) target.clone();
 		trapStates.or(inf);