diff --git a/prism/src/pta/DBM.java b/prism/src/pta/DBM.java
index f6a57f0f..ba4561a9 100644
--- a/prism/src/pta/DBM.java
+++ b/prism/src/pta/DBM.java
@@ -320,7 +320,7 @@ public class DBM extends Zone
 	{
 		int i, n;
 		n = pta.numClocks;
-		for (i = 0; i < n + 1; i++) {
+		for (i = 1; i < n + 1; i++) {
 			if (!DB.isInfty(d[i][0])) {
 				return false;
 			}
diff --git a/prism/src/pta/DBMList.java b/prism/src/pta/DBMList.java
index 1a6bde71..6bc72c0c 100644
--- a/prism/src/pta/DBMList.java
+++ b/prism/src/pta/DBMList.java
@@ -353,7 +353,7 @@ public class DBMList extends NCZone
 	{
 		int i, n;
 		n = pta.numClocks;
-		for (i = 0; i < n + 1; i++) {
+		for (i = 1; i < n + 1; i++) {
 			if (!clockIsUnbounded(i)) {
 				return false;
 			}