diff --git a/src/main/java/org/gcube/accounting/analytics/persistence/AccountingPersistenceBackendQuery.java b/src/main/java/org/gcube/accounting/analytics/persistence/AccountingPersistenceBackendQuery.java
index ded6c7d..86be94f 100644
--- a/src/main/java/org/gcube/accounting/analytics/persistence/AccountingPersistenceBackendQuery.java
+++ b/src/main/java/org/gcube/accounting/analytics/persistence/AccountingPersistenceBackendQuery.java
@@ -72,7 +72,7 @@ public interface AccountingPersistenceBackendQuery {
 	 * If the list contains more than one filter with the same key an Exception is thrown 
 	 * when trying to query.
 	 */
-	public void setFilters(Collection<Filter> filters);
+	public void setFilters(Collection<? extends Filter> filters);
 	
 	/**
 	 * Query the persistence obtaining a Map where the date is the key and the
diff --git a/src/main/java/org/gcube/accounting/analytics/persistence/AccountingPersistenceQuery.java b/src/main/java/org/gcube/accounting/analytics/persistence/AccountingPersistenceQuery.java
index 1cf94d9..2d6336a 100644
--- a/src/main/java/org/gcube/accounting/analytics/persistence/AccountingPersistenceQuery.java
+++ b/src/main/java/org/gcube/accounting/analytics/persistence/AccountingPersistenceQuery.java
@@ -61,7 +61,7 @@ public class AccountingPersistenceQuery implements AccountingPersistenceBackendQ
 	protected TemporalConstraint temporalConstraint;
 	
 	protected Set<String> contexts;
-	protected Collection<Filter> filters;
+	protected Collection<? extends Filter> filters;
 	
 	protected ObjectMapper objectMapper;
 	
@@ -91,7 +91,7 @@ public class AccountingPersistenceQuery implements AccountingPersistenceBackendQ
 	}
 	
 	@Override
-	public void setFilters(Collection<Filter> filters) {
+	public void setFilters(Collection<? extends Filter> filters) {
 		this.filters = filters;
 		accountingPersistenceBackendQuery.setFilters(filters);
 	}