diff --git a/src/main/java/eu/dnetlib/validator2/validation/guideline/openaire/F3_01M.java b/src/main/java/eu/dnetlib/validator2/validation/guideline/openaire/F3_01M.java
index 2c89b66..8cc98d7 100644
--- a/src/main/java/eu/dnetlib/validator2/validation/guideline/openaire/F3_01M.java
+++ b/src/main/java/eu/dnetlib/validator2/validation/guideline/openaire/F3_01M.java
@@ -24,7 +24,7 @@ public final class F3_01M extends AbstractOpenAireProfile {
     };
  
     private static final ElementSpec F3_01M_SPEC_1 = Builders.
-            forMandatoryElement("identifier", ONE).
+            forMandatoryElement("identifier", ONE_TO_N).
 //            withMandatoryAttribute("identifierType", new PIDCheckValuePredicate()).
             withMandatoryAttribute("identifierType", RESOURCE_IDENTIFIER_TYPES).
             build();