diff --git a/prism/src/automata/DA.java b/prism/src/automata/DA.java
index ee02a2ff..034d62b2 100644
--- a/prism/src/automata/DA.java
+++ b/prism/src/automata/DA.java
@@ -73,6 +73,14 @@ public class DA<Symbol, Acceptance extends AcceptanceOmega>
 		}
 	}
 
+	/**
+	 * Construct a DRA with zero states, use addState to add states.
+	 */
+	public DA()
+	{
+		this(0);
+	}
+
 	/**
 	 * Construct a DRA of fixed size (i.e. fixed number of states).
 	 */
@@ -109,6 +117,17 @@ public class DA<Symbol, Acceptance extends AcceptanceOmega>
 
 	// Mutators
 
+	/**
+	 * Add a state.
+	 * @return index of the fresh state
+	 */
+	public int addState()
+	{
+		edges.add(new ArrayList<Edge>());
+		size++;
+		return size-1;
+	}
+
 	/**
 	 * Set the start state (index)
 	 */