diff --git a/mica-search/src/main/java/org/obiba/mica/search/queries/rql/RQLQueryWrapper.java b/mica-search/src/main/java/org/obiba/mica/search/queries/rql/RQLQueryWrapper.java
index 9db56e9d32..aaf05a32b7 100644
--- a/mica-search/src/main/java/org/obiba/mica/search/queries/rql/RQLQueryWrapper.java
+++ b/mica-search/src/main/java/org/obiba/mica/search/queries/rql/RQLQueryWrapper.java
@@ -502,7 +502,10 @@ public List<SortBuilder> visit(ASTNode node) {
             List<SortBuilder> sortBuilders = Lists.newArrayList();
             if (node.getArgumentsSize() >= 1) {
               for(int i = 0; i < node.getArgumentsSize(); i++) {
-                sortBuilders.add(processArgument(node.getArgument(i).toString()));
+                SortBuilder sortBuilder = processArgument(node.getArgument(i).toString());
+                ((FieldSortBuilder) sortBuilder).unmappedType("string");
+                sortBuilder.missing("_last");
+                sortBuilders.add(sortBuilder);
               }
             }
             return sortBuilders;
diff --git a/mica-search/src/test/java/org/obiba/mica/search/queries/rql/RQLQueryWrapperTest.java b/mica-search/src/test/java/org/obiba/mica/search/queries/rql/RQLQueryWrapperTest.java
index 7b3f8678a9..f47c58d774 100644
--- a/mica-search/src/test/java/org/obiba/mica/search/queries/rql/RQLQueryWrapperTest.java
+++ b/mica-search/src/test/java/org/obiba/mica/search/queries/rql/RQLQueryWrapperTest.java
@@ -343,7 +343,9 @@ public void test_rql_query_term_and_limit_and_sort() throws IOException {
     assertThat(rqlQueryWrapper.getSize()).isEqualTo(4);
     String expectedSort = "\n" +
       "\"name\"{\n" +
-      "  \"order\" : \"desc\"\n" +
+      "  \"order\" : \"desc\",\n" +
+      "  \"missing\" : \"_last\",\n" +
+      "  \"unmapped_type\" : \"string\"\n" +
       "}";
     assertThat(rqlQueryWrapper.getSortBuilders().get(0).toString()).isEqualTo(expectedSort);
   }