Index: applications/editors/josm/plugins/wikipedia/src/org/wikipedia/WikipediaApp.java
===================================================================
--- applications/editors/josm/plugins/wikipedia/src/org/wikipedia/WikipediaApp.java	(revision 33017)
+++ applications/editors/josm/plugins/wikipedia/src/org/wikipedia/WikipediaApp.java	(revision 33066)
@@ -18,4 +18,5 @@
 import java.util.Objects;
 import java.util.TreeMap;
+import java.util.TreeSet;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -194,5 +195,6 @@
     public static Map<String, String> getWikidataForArticles(String wikipediaLang, List<String> articles) {
         if (articles.size() > 50) {
-            return partitionList(articles, 50).stream()
+            final List<String> withoutDuplicates = new ArrayList<>(new TreeSet<>(articles));
+            return partitionList(withoutDuplicates, 50).stream()
                     .flatMap(chunk -> getWikidataForArticles(wikipediaLang, chunk).entrySet().stream())
                     .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));