diff --git a/prism/src/prism/OpRelOpBound.java b/prism/src/prism/OpRelOpBound.java
index 2ba1ada8..c2dfef71 100644
--- a/prism/src/prism/OpRelOpBound.java
+++ b/prism/src/prism/OpRelOpBound.java
@@ -122,6 +122,6 @@ public class OpRelOpBound
 	@Override
 	public String toString()
 	{
-		return op + relOp.toString() + bound;
+		return op + relOp.toString() + (isNumeric() ? "?" : bound);
 	}
 }