diff --git a/dhp-workflows/dhp-dedup-openaire/src/main/java/eu/dnetlib/dhp/oa/dedup/Deduper.java b/dhp-workflows/dhp-dedup-openaire/src/main/java/eu/dnetlib/dhp/oa/dedup/Deduper.java
index 5e8a50fcc..68201677e 100644
--- a/dhp-workflows/dhp-dedup-openaire/src/main/java/eu/dnetlib/dhp/oa/dedup/Deduper.java
+++ b/dhp-workflows/dhp-dedup-openaire/src/main/java/eu/dnetlib/dhp/oa/dedup/Deduper.java
@@ -51,8 +51,8 @@ public class Deduper implements Serializable {
 					.map(it -> Block.from(it, a))
 					.collect(Collectors.toList())
 					.iterator())
-			.filter(b -> b.getDocuments().size() > 1)
 			.mapToPair(block -> new Tuple2<>(block.getKey(), block))
-			.reduceByKey((b1, b2) -> Block.from(b1, b2, of, maxQueueSize));
+			.reduceByKey((b1, b2) -> Block.from(b1, b2, of, maxQueueSize))
+			.filter(b -> b._2().getDocuments().size() > 1);
 	}
 }