diff --git a/prism/src/prism/NondetModelChecker.java b/prism/src/prism/NondetModelChecker.java
index 5b890b4f..86c74e12 100644
--- a/prism/src/prism/NondetModelChecker.java
+++ b/prism/src/prism/NondetModelChecker.java
@@ -1609,9 +1609,15 @@ public class NondetModelChecker implements ModelChecker
 			}
 			catch (PrismException e) {
 				throw e;
+				JDD.Deref(inf);
+				JDD.Deref(maybe);
 			}
 		}
 		
+		// derefs
+		JDD.Deref(inf);
+		JDD.Deref(maybe);
+		
 		return rewards;
 	}
 }