diff --git a/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/oa/graph/raw/common/OafMapperUtils.java b/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/oa/graph/raw/common/OafMapperUtils.java
index 8ede40773..63db13b8f 100644
--- a/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/oa/graph/raw/common/OafMapperUtils.java
+++ b/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/oa/graph/raw/common/OafMapperUtils.java
@@ -4,7 +4,11 @@ package eu.dnetlib.dhp.oa.graph.raw.common;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Map;
 import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Function;
+import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
 import org.apache.commons.lang3.StringUtils;
@@ -57,6 +61,7 @@ public class OafMapperUtils {
 			.stream(values)
 			.map(v -> field(v, info))
 			.filter(Objects::nonNull)
+			.filter(distinctByKey(f -> f.getValue()))
 			.collect(Collectors.toList());
 	}
 
@@ -65,6 +70,7 @@ public class OafMapperUtils {
 			.stream()
 			.map(v -> field(v, info))
 			.filter(Objects::nonNull)
+			.filter(distinctByKey(f -> f.getValue()))
 			.collect(Collectors.toList());
 	}
 
@@ -237,4 +243,10 @@ public class OafMapperUtils {
 	public static String asString(final Object o) {
 		return o == null ? "" : o.toString();
 	}
+
+	public static <T> Predicate<T> distinctByKey(
+		final Function<? super T, ?> keyExtractor) {
+		final Map<Object, Boolean> seen = new ConcurrentHashMap<>();
+		return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
+	}
 }
diff --git a/dhp-workflows/dhp-graph-mapper/src/test/java/eu/dnetlib/dhp/oa/graph/raw/MappersTest.java b/dhp-workflows/dhp-graph-mapper/src/test/java/eu/dnetlib/dhp/oa/graph/raw/MappersTest.java
index b1f0ecf0d..ffd21c86e 100644
--- a/dhp-workflows/dhp-graph-mapper/src/test/java/eu/dnetlib/dhp/oa/graph/raw/MappersTest.java
+++ b/dhp-workflows/dhp-graph-mapper/src/test/java/eu/dnetlib/dhp/oa/graph/raw/MappersTest.java
@@ -71,6 +71,7 @@ public class MappersTest {
 		assertValidId(p.getCollectedfrom().get(0).getKey());
 		assertTrue(StringUtils.isNotBlank(p.getTitle().get(0).getValue()));
 		assertFalse(p.getDataInfo().getInvisible());
+		assertTrue(p.getSource().size() == 1);
 
 		assertTrue(p.getAuthor().size() > 0);
 		final Optional<Author> author = p
@@ -79,6 +80,7 @@ public class MappersTest {
 			.filter(a -> a.getPid() != null && !a.getPid().isEmpty())
 			.findFirst();
 		assertTrue(author.isPresent());
+
 		final StructuredProperty pid = author
 			.get()
 			.getPid()
diff --git a/dhp-workflows/dhp-graph-mapper/src/test/resources/eu/dnetlib/dhp/oa/graph/raw/oaf_record.xml b/dhp-workflows/dhp-graph-mapper/src/test/resources/eu/dnetlib/dhp/oa/graph/raw/oaf_record.xml
index ead22aa96..be78bf35c 100644
--- a/dhp-workflows/dhp-graph-mapper/src/test/resources/eu/dnetlib/dhp/oa/graph/raw/oaf_record.xml
+++ b/dhp-workflows/dhp-graph-mapper/src/test/resources/eu/dnetlib/dhp/oa/graph/raw/oaf_record.xml
@@ -34,6 +34,8 @@
     <dc:relation>info:eu-repo/semantics/altIdentifier/eissn/2367-8194</dc:relation>
     <dc:relation>info:eu-repo/grantAgreement/EC/FP7/226852</dc:relation>
     <dc:source>One Ecosystem 2: e13718</dc:source>
+    <dc:source>One Ecosystem 2: e13718</dc:source>
+    <dc:source>One Ecosystem 2: e13718</dc:source>
     <dc:subject>Ecosystem Services hotspots</dc:subject>
     <dc:subject>Natura 2000</dc:subject>
     <dc:subject>Quiet Protected Areas</dc:subject>