diff --git a/core/src/main/java/org/elasticsearch/common/xcontent/XContent.java b/core/src/main/java/org/elasticsearch/common/xcontent/XContent.java
index c73f5f19d25..72210f09d9b 100644
--- a/core/src/main/java/org/elasticsearch/common/xcontent/XContent.java
+++ b/core/src/main/java/org/elasticsearch/common/xcontent/XContent.java
@@ -19,6 +19,7 @@
 
 package org.elasticsearch.common.xcontent;
 
+import org.elasticsearch.common.Booleans;
 import org.elasticsearch.common.bytes.BytesReference;
 
 import java.io.IOException;
@@ -33,6 +34,27 @@ import java.util.Set;
  */
 public interface XContent {
 
+    /*
+     * NOTE: This comment is only meant for maintainers of the Elasticsearch code base and is intentionally not a Javadoc comment as it
+     *       describes an undocumented system property.
+     *
+     *
+     * Determines whether the XContent parser will always check for duplicate keys. This behavior is enabled by default but
+     * can be disabled by setting the otherwise undocumented system property "es.xcontent.strict_duplicate_detection to "false".
+     *
+     * Before we've enabled this mode, we had custom duplicate checks in various parts of the code base. As the user can still disable this
+     * mode and fall back to the legacy duplicate checks, we still need to keep the custom duplicate checks around and we also need to keep
+     * the tests around.
+     *
+     * If this fallback via system property is removed one day in the future you can remove all tests that call this method and also remove
+     * the corresponding custom duplicate check code.
+     *
+     */
+    static boolean isStrictDuplicateDetectionEnabled() {
+        // Don't allow duplicate keys in JSON content by default but let the user opt out
+        return Booleans.parseBooleanExact(System.getProperty("es.xcontent.strict_duplicate_detection", "true"));
+    }
+
     /**
      * The type this content handles and produces.
      */
diff --git a/core/src/main/java/org/elasticsearch/common/xcontent/cbor/CborXContent.java b/core/src/main/java/org/elasticsearch/common/xcontent/cbor/CborXContent.java
index 4224b5328a7..d79173cfc2b 100644
--- a/core/src/main/java/org/elasticsearch/common/xcontent/cbor/CborXContent.java
+++ b/core/src/main/java/org/elasticsearch/common/xcontent/cbor/CborXContent.java
@@ -21,6 +21,7 @@ package org.elasticsearch.common.xcontent.cbor;
 
 import com.fasterxml.jackson.core.JsonEncoding;
 import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.JsonParser;
 import com.fasterxml.jackson.dataformat.cbor.CBORFactory;
 import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.common.bytes.BytesReference;
@@ -54,6 +55,7 @@ public class CborXContent implements XContent {
         cborFactory.configure(CBORFactory.Feature.FAIL_ON_SYMBOL_HASH_OVERFLOW, false); // this trips on many mappings now...
         // Do not automatically close unclosed objects/arrays in com.fasterxml.jackson.dataformat.cbor.CBORGenerator#close() method
         cborFactory.configure(JsonGenerator.Feature.AUTO_CLOSE_JSON_CONTENT, false);
+        cborFactory.configure(JsonParser.Feature.STRICT_DUPLICATE_DETECTION, XContent.isStrictDuplicateDetectionEnabled());
         cborXContent = new CborXContent();
     }
 
diff --git a/core/src/main/java/org/elasticsearch/common/xcontent/json/JsonXContent.java b/core/src/main/java/org/elasticsearch/common/xcontent/json/JsonXContent.java
index 4657a554099..1b0b351e6ef 100644
--- a/core/src/main/java/org/elasticsearch/common/xcontent/json/JsonXContent.java
+++ b/core/src/main/java/org/elasticsearch/common/xcontent/json/JsonXContent.java
@@ -23,7 +23,6 @@ import com.fasterxml.jackson.core.JsonEncoding;
 import com.fasterxml.jackson.core.JsonFactory;
 import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.core.JsonParser;
-import org.elasticsearch.common.Booleans;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.io.FastStringReader;
 import org.elasticsearch.common.xcontent.XContent;
@@ -50,27 +49,6 @@ public class JsonXContent implements XContent {
 
     public static final JsonXContent jsonXContent;
 
-    /*
-     * NOTE: This comment is only meant for maintainers of the Elasticsearch code base and is intentionally not a Javadoc comment as it
-     *       describes an undocumented system property.
-     *
-     *
-     * Determines whether the JSON parser will always check for duplicate keys in JSON content. This behavior is enabled by default but
-     * can be disabled by setting the otherwise undocumented system property "es.json.strict_duplicate_detection" to "false".
-     *
-     * Before we've enabled this mode, we had custom duplicate checks in various parts of the code base. As the user can still disable this
-     * mode and fall back to the legacy duplicate checks, we still need to keep the custom duplicate checks around and we also need to keep
-     * the tests around.
-     *
-     * If this fallback via system property is removed one day in the future you can remove all tests that call this method and also remove
-     * the corresponding custom duplicate check code.
-     *
-     */
-    public static boolean isStrictDuplicateDetectionEnabled() {
-        // Don't allow duplicate keys in JSON content by default but let the user opt out
-        return Booleans.parseBooleanExact(System.getProperty("es.json.strict_duplicate_detection", "true"));
-    }
-
     static {
         jsonFactory = new JsonFactory();
         jsonFactory.configure(JsonGenerator.Feature.QUOTE_FIELD_NAMES, true);
@@ -78,7 +56,7 @@ public class JsonXContent implements XContent {
         jsonFactory.configure(JsonFactory.Feature.FAIL_ON_SYMBOL_HASH_OVERFLOW, false); // this trips on many mappings now...
         // Do not automatically close unclosed objects/arrays in com.fasterxml.jackson.core.json.UTF8JsonGenerator#close() method
         jsonFactory.configure(JsonGenerator.Feature.AUTO_CLOSE_JSON_CONTENT, false);
-        jsonFactory.configure(JsonParser.Feature.STRICT_DUPLICATE_DETECTION, isStrictDuplicateDetectionEnabled());
+        jsonFactory.configure(JsonParser.Feature.STRICT_DUPLICATE_DETECTION, XContent.isStrictDuplicateDetectionEnabled());
         jsonXContent = new JsonXContent();
     }
 
diff --git a/core/src/main/java/org/elasticsearch/common/xcontent/smile/SmileXContent.java b/core/src/main/java/org/elasticsearch/common/xcontent/smile/SmileXContent.java
index 94ac9b94356..643326cd82f 100644
--- a/core/src/main/java/org/elasticsearch/common/xcontent/smile/SmileXContent.java
+++ b/core/src/main/java/org/elasticsearch/common/xcontent/smile/SmileXContent.java
@@ -21,6 +21,7 @@ package org.elasticsearch.common.xcontent.smile;
 
 import com.fasterxml.jackson.core.JsonEncoding;
 import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.JsonParser;
 import com.fasterxml.jackson.dataformat.smile.SmileFactory;
 import com.fasterxml.jackson.dataformat.smile.SmileGenerator;
 import org.elasticsearch.common.bytes.BytesReference;
@@ -55,6 +56,7 @@ public class SmileXContent implements XContent {
         smileFactory.configure(SmileFactory.Feature.FAIL_ON_SYMBOL_HASH_OVERFLOW, false); // this trips on many mappings now...
         // Do not automatically close unclosed objects/arrays in com.fasterxml.jackson.dataformat.smile.SmileGenerator#close() method
         smileFactory.configure(JsonGenerator.Feature.AUTO_CLOSE_JSON_CONTENT, false);
+        smileFactory.configure(JsonParser.Feature.STRICT_DUPLICATE_DETECTION, XContent.isStrictDuplicateDetectionEnabled());
         smileXContent = new SmileXContent();
     }
 
diff --git a/core/src/main/java/org/elasticsearch/common/xcontent/yaml/YamlXContent.java b/core/src/main/java/org/elasticsearch/common/xcontent/yaml/YamlXContent.java
index 54da03118d7..7413f05f583 100644
--- a/core/src/main/java/org/elasticsearch/common/xcontent/yaml/YamlXContent.java
+++ b/core/src/main/java/org/elasticsearch/common/xcontent/yaml/YamlXContent.java
@@ -20,6 +20,7 @@
 package org.elasticsearch.common.xcontent.yaml;
 
 import com.fasterxml.jackson.core.JsonEncoding;
+import com.fasterxml.jackson.core.JsonParser;
 import com.fasterxml.jackson.dataformat.yaml.YAMLFactory;
 import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.common.bytes.BytesReference;
@@ -50,6 +51,7 @@ public class YamlXContent implements XContent {
 
     static {
         yamlFactory = new YAMLFactory();
+        yamlFactory.configure(JsonParser.Feature.STRICT_DUPLICATE_DETECTION, XContent.isStrictDuplicateDetectionEnabled());
         yamlXContent = new YamlXContent();
     }
 
diff --git a/core/src/test/java/org/elasticsearch/common/settings/loader/JsonSettingsLoaderTests.java b/core/src/test/java/org/elasticsearch/common/settings/loader/JsonSettingsLoaderTests.java
index 70439ef8bf9..d917c0d12c0 100644
--- a/core/src/test/java/org/elasticsearch/common/settings/loader/JsonSettingsLoaderTests.java
+++ b/core/src/test/java/org/elasticsearch/common/settings/loader/JsonSettingsLoaderTests.java
@@ -22,7 +22,7 @@ package org.elasticsearch.common.settings.loader;
 import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.settings.SettingsException;
-import org.elasticsearch.common.xcontent.json.JsonXContent;
+import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.test.ESTestCase;
 
 import static org.hamcrest.CoreMatchers.containsString;
@@ -49,8 +49,8 @@ public class JsonSettingsLoaderTests extends ESTestCase {
     }
 
     public void testDuplicateKeysThrowsException() {
-        assumeFalse("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
         final String json = "{\"foo\":\"bar\",\"foo\":\"baz\"}";
         final SettingsException e = expectThrows(SettingsException.class, () -> Settings.builder().loadFromSource(json).build());
         assertEquals(e.getCause().getClass(), ElasticsearchParseException.class);
diff --git a/core/src/test/java/org/elasticsearch/common/settings/loader/YamlSettingsLoaderTests.java b/core/src/test/java/org/elasticsearch/common/settings/loader/YamlSettingsLoaderTests.java
index 7c956de8f9a..eeb2df7e1d6 100644
--- a/core/src/test/java/org/elasticsearch/common/settings/loader/YamlSettingsLoaderTests.java
+++ b/core/src/test/java/org/elasticsearch/common/settings/loader/YamlSettingsLoaderTests.java
@@ -22,6 +22,7 @@ package org.elasticsearch.common.settings.loader;
 import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.settings.SettingsException;
+import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.test.ESTestCase;
 
 import java.nio.charset.StandardCharsets;
@@ -68,6 +69,9 @@ public class YamlSettingsLoaderTests extends ESTestCase {
     }
 
     public void testDuplicateKeysThrowsException() {
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
+
         String yaml = "foo: bar\nfoo: baz";
         SettingsException e = expectThrows(SettingsException.class, () -> {
             Settings.builder().loadFromSource(yaml);
diff --git a/core/src/test/java/org/elasticsearch/common/xcontent/BaseXContentTestCase.java b/core/src/test/java/org/elasticsearch/common/xcontent/BaseXContentTestCase.java
index 57e9e0d5216..1c0a92dbd74 100644
--- a/core/src/test/java/org/elasticsearch/common/xcontent/BaseXContentTestCase.java
+++ b/core/src/test/java/org/elasticsearch/common/xcontent/BaseXContentTestCase.java
@@ -22,6 +22,7 @@ package org.elasticsearch.common.xcontent;
 import com.fasterxml.jackson.core.JsonGenerationException;
 import com.fasterxml.jackson.core.JsonGenerator;
 
+import com.fasterxml.jackson.core.JsonParseException;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.Constants;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
@@ -66,6 +67,7 @@ import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.notNullValue;
+import static org.hamcrest.Matchers.startsWith;
 
 public abstract class BaseXContentTestCase extends ESTestCase {
 
@@ -984,6 +986,22 @@ public abstract class BaseXContentTestCase extends ESTestCase {
         assertThat(e.getMessage(), containsString("Object has already been built and is self-referencing itself"));
     }
 
+    public void testChecksForDuplicates() throws Exception {
+        assumeTrue("Test only makes sense if XContent parser has strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
+
+        BytesReference bytes = builder()
+                .startObject()
+                    .field("key", 1)
+                    .field("key", 2)
+                .endObject()
+            .bytes();
+
+        JsonParseException pex = expectThrows(JsonParseException.class, () -> createParser(xcontentType().xContent(), bytes).map());
+        assertThat(pex.getMessage(), startsWith("Duplicate field 'key'"));
+    }
+
+
     private static void expectUnclosedException(ThrowingRunnable runnable) {
         IllegalStateException e = expectThrows(IllegalStateException.class, runnable);
         assertThat(e.getMessage(), containsString("Failed to close the XContentBuilder"));
diff --git a/core/src/test/java/org/elasticsearch/common/xcontent/ConstructingObjectParserTests.java b/core/src/test/java/org/elasticsearch/common/xcontent/ConstructingObjectParserTests.java
index 387efdb5e50..6cae59391c5 100644
--- a/core/src/test/java/org/elasticsearch/common/xcontent/ConstructingObjectParserTests.java
+++ b/core/src/test/java/org/elasticsearch/common/xcontent/ConstructingObjectParserTests.java
@@ -169,8 +169,8 @@ public class ConstructingObjectParserTests extends ESTestCase {
     }
 
     public void testRepeatedConstructorParam() throws IOException {
-        assumeFalse("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
         XContentParser parser = createParser(JsonXContent.jsonXContent,
                   "{\n"
                 + "  \"vegetable\": 1,\n"
diff --git a/core/src/test/java/org/elasticsearch/common/xcontent/json/JsonXContentTests.java b/core/src/test/java/org/elasticsearch/common/xcontent/json/JsonXContentTests.java
index b4549830432..4a79ddb4ec6 100644
--- a/core/src/test/java/org/elasticsearch/common/xcontent/json/JsonXContentTests.java
+++ b/core/src/test/java/org/elasticsearch/common/xcontent/json/JsonXContentTests.java
@@ -22,7 +22,6 @@ package org.elasticsearch.common.xcontent.json;
 import com.fasterxml.jackson.core.JsonFactory;
 import com.fasterxml.jackson.core.JsonGenerator;
 
-import com.fasterxml.jackson.core.JsonParseException;
 import org.elasticsearch.common.xcontent.BaseXContentTestCase;
 import org.elasticsearch.common.xcontent.XContentType;
 
@@ -40,13 +39,4 @@ public class JsonXContentTests extends BaseXContentTestCase {
         JsonGenerator generator = new JsonFactory().createGenerator(os);
         doTestBigInteger(generator, os);
     }
-
-    public void testChecksForDuplicates() throws Exception {
-        assumeTrue("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
-
-        JsonParseException pex = expectThrows(JsonParseException.class,
-            () -> XContentType.JSON.xContent().createParser("{ \"key\": 1, \"key\": 2 }").map());
-        assertEquals("Duplicate field 'key'", pex.getMessage());
-    }
 }
diff --git a/core/src/test/java/org/elasticsearch/index/query/BoolQueryBuilderTests.java b/core/src/test/java/org/elasticsearch/index/query/BoolQueryBuilderTests.java
index 8e04ec7f553..13854ffc1e2 100644
--- a/core/src/test/java/org/elasticsearch/index/query/BoolQueryBuilderTests.java
+++ b/core/src/test/java/org/elasticsearch/index/query/BoolQueryBuilderTests.java
@@ -26,6 +26,7 @@ import org.apache.lucene.search.MatchAllDocsQuery;
 import org.apache.lucene.search.Query;
 import org.elasticsearch.common.ParseFieldMatcher;
 import org.elasticsearch.common.ParsingException;
+import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentType;
@@ -340,8 +341,8 @@ public class BoolQueryBuilderTests extends AbstractQueryTestCase<BoolQueryBuilde
      * test that two queries in object throws error
      */
     public void testTooManyQueriesInObject() throws IOException {
-        assumeFalse("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
         String clauseType = randomFrom("must", "should", "must_not", "filter");
         // should also throw error if invalid query is preceded by a valid one
         String query = "{\n" +
diff --git a/core/src/test/java/org/elasticsearch/index/query/ConstantScoreQueryBuilderTests.java b/core/src/test/java/org/elasticsearch/index/query/ConstantScoreQueryBuilderTests.java
index 9aa151e985d..d8925af70ae 100644
--- a/core/src/test/java/org/elasticsearch/index/query/ConstantScoreQueryBuilderTests.java
+++ b/core/src/test/java/org/elasticsearch/index/query/ConstantScoreQueryBuilderTests.java
@@ -22,6 +22,7 @@ package org.elasticsearch.index.query;
 import org.apache.lucene.search.ConstantScoreQuery;
 import org.apache.lucene.search.Query;
 import org.elasticsearch.common.ParsingException;
+import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
 import org.elasticsearch.search.internal.SearchContext;
 import org.elasticsearch.test.AbstractQueryTestCase;
@@ -66,8 +67,8 @@ public class ConstantScoreQueryBuilderTests extends AbstractQueryTestCase<Consta
      * test that multiple "filter" elements causes {@link ParsingException}
      */
     public void testMultipleFilterElements() throws IOException {
-        assumeFalse("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
         String queryString = "{ \"" + ConstantScoreQueryBuilder.NAME + "\" : {\n" +
                                     "\"filter\" : { \"term\": { \"foo\": \"a\" } },\n" +
                                     "\"filter\" : { \"term\": { \"foo\": \"x\" } },\n" +
diff --git a/core/src/test/java/org/elasticsearch/index/query/functionscore/FunctionScoreQueryBuilderTests.java b/core/src/test/java/org/elasticsearch/index/query/functionscore/FunctionScoreQueryBuilderTests.java
index 0f79e90aa04..50c63e66f58 100644
--- a/core/src/test/java/org/elasticsearch/index/query/functionscore/FunctionScoreQueryBuilderTests.java
+++ b/core/src/test/java/org/elasticsearch/index/query/functionscore/FunctionScoreQueryBuilderTests.java
@@ -36,6 +36,7 @@ import org.elasticsearch.common.lucene.search.function.FiltersFunctionScoreQuery
 import org.elasticsearch.common.lucene.search.function.FunctionScoreQuery;
 import org.elasticsearch.common.lucene.search.function.WeightFactorFunction;
 import org.elasticsearch.common.unit.DistanceUnit;
+import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
@@ -739,8 +740,8 @@ public class FunctionScoreQueryBuilderTests extends AbstractQueryTestCase<Functi
     }
 
     public void testMalformedQueryMultipleQueryElements() throws IOException {
-        assumeFalse("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
         String json = "{\n" +
                 "    \"function_score\":{\n" +
                 "        \"query\":{\n" +
diff --git a/core/src/test/java/org/elasticsearch/search/aggregations/AggregatorParsingTests.java b/core/src/test/java/org/elasticsearch/search/aggregations/AggregatorParsingTests.java
index 87ca8ffdd93..26b3dd6f8f2 100644
--- a/core/src/test/java/org/elasticsearch/search/aggregations/AggregatorParsingTests.java
+++ b/core/src/test/java/org/elasticsearch/search/aggregations/AggregatorParsingTests.java
@@ -22,6 +22,7 @@ package org.elasticsearch.search.aggregations;
 import org.elasticsearch.common.ParseFieldMatcher;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
@@ -104,8 +105,8 @@ public class AggregatorParsingTests extends ESTestCase {
     }
 
     public void testTwoAggs() throws Exception {
-        assumeFalse("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
         XContentBuilder source = JsonXContent.contentBuilder()
                 .startObject()
                     .startObject("by_date")
@@ -180,8 +181,8 @@ public class AggregatorParsingTests extends ESTestCase {
     }
 
     public void testSameAggregationName() throws Exception {
-        assumeFalse("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
         final String name = randomAsciiOfLengthBetween(1, 10);
         XContentBuilder source = JsonXContent.contentBuilder()
                 .startObject()
diff --git a/core/src/test/java/org/elasticsearch/search/suggest/phrase/DirectCandidateGeneratorTests.java b/core/src/test/java/org/elasticsearch/search/suggest/phrase/DirectCandidateGeneratorTests.java
index 41713bbce94..27ec964aa4b 100644
--- a/core/src/test/java/org/elasticsearch/search/suggest/phrase/DirectCandidateGeneratorTests.java
+++ b/core/src/test/java/org/elasticsearch/search/suggest/phrase/DirectCandidateGeneratorTests.java
@@ -23,6 +23,7 @@ import org.elasticsearch.common.ParseFieldMatcher;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentParser;
@@ -149,7 +150,7 @@ public class DirectCandidateGeneratorTests extends ESTestCase{
                 "Required [field]");
 
         // test two fieldnames
-        if (JsonXContent.isStrictDuplicateDetectionEnabled()) {
+        if (XContent.isStrictDuplicateDetectionEnabled()) {
             logger.info("Skipping test as it uses a custom duplicate check that is obsolete when strict duplicate checks are enabled.");
         } else {
             directGenerator = "{ \"field\" : \"f1\", \"field\" : \"f2\" }";
diff --git a/docs/reference/migration/migrate_6_0/rest.asciidoc b/docs/reference/migration/migrate_6_0/rest.asciidoc
index 67931315893..dcbc289300e 100644
--- a/docs/reference/migration/migrate_6_0/rest.asciidoc
+++ b/docs/reference/migration/migrate_6_0/rest.asciidoc
@@ -8,10 +8,10 @@ This feature was removed in the 5.x series, but a backwards-compatibility layer
 system property `elasticsearch.json.allow_unquoted_field_names`. This backwards-compatibility layer
 has been removed in Elasticsearch 6.0.0.
 
-==== Duplicate Keys in JSON
+==== Duplicate Keys in JSON, CBOR, Yaml and Smile
 
-In previous versions of Elasticsearch, JSON documents were allowed to contain duplicate keys. Elasticsearch 6.0.0
- enforces that all keys are unique.
+In previous versions of Elasticsearch, documents were allowed to contain duplicate keys. Elasticsearch 6.0.0
+ enforces that all keys are unique. This applies to all content types: JSON, CBOR, Yaml and Smile.
 
 ==== Analyze API changes
 
diff --git a/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/parser/AbstractClientYamlTestFragmentParserTestCase.java b/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/parser/AbstractClientYamlTestFragmentParserTestCase.java
index 4346115c184..3b0859d2d8b 100644
--- a/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/parser/AbstractClientYamlTestFragmentParserTestCase.java
+++ b/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/parser/AbstractClientYamlTestFragmentParserTestCase.java
@@ -36,8 +36,11 @@ public abstract class AbstractClientYamlTestFragmentParserTestCase extends ESTes
     @After
     public void tearDown() throws Exception {
         super.tearDown();
-        //this is the way to make sure that we consumed the whole yaml
-        assertThat(parser.currentToken(), nullValue());
-        parser.close();
+        // test may be skipped so we did not create a parser instance
+        if (parser != null) {
+            //this is the way to make sure that we consumed the whole yaml
+            assertThat(parser.currentToken(), nullValue());
+            parser.close();
+        }
     }
 }
diff --git a/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/parser/DoSectionParserTests.java b/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/parser/DoSectionParserTests.java
index 8992b3abde4..6057de6c702 100644
--- a/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/parser/DoSectionParserTests.java
+++ b/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/parser/DoSectionParserTests.java
@@ -18,6 +18,7 @@
  */
 package org.elasticsearch.test.rest.yaml.parser;
 
+import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.yaml.YamlXContent;
 import org.elasticsearch.test.rest.yaml.section.ApiCallSection;
@@ -126,6 +127,9 @@ public class DoSectionParserTests extends AbstractClientYamlTestFragmentParserTe
     }
 
     public void testParseDoSectionWithJsonMultipleBodiesRepeatedProperty() throws Exception {
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
+
         String[] bodies = new String[] {
                 "{ \"index\": { \"_index\":\"test_index\", \"_type\":\"test_type\", \"_id\":\"test_id\" } }",
                 "{ \"f1\":\"v1\", \"f2\":42 }",
@@ -216,6 +220,9 @@ public class DoSectionParserTests extends AbstractClientYamlTestFragmentParserTe
     }
 
     public void testParseDoSectionWithYamlMultipleBodiesRepeatedProperty() throws Exception {
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
+
         parser = createParser(YamlXContent.yamlXContent,
                 "bulk:\n" +
                 "    refresh: true\n" +
diff --git a/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/restspec/ClientYamlSuiteRestApiParserFailingTests.java b/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/restspec/ClientYamlSuiteRestApiParserFailingTests.java
index d60fc66b7ec..a1d713db127 100644
--- a/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/restspec/ClientYamlSuiteRestApiParserFailingTests.java
+++ b/test/framework/src/test/java/org/elasticsearch/test/rest/yaml/restspec/ClientYamlSuiteRestApiParserFailingTests.java
@@ -18,6 +18,7 @@
  */
 package org.elasticsearch.test.rest.yaml.restspec;
 
+import org.elasticsearch.common.xcontent.XContent;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
 import org.elasticsearch.common.xcontent.yaml.YamlXContent;
@@ -72,8 +73,8 @@ public class ClientYamlSuiteRestApiParserFailingTests extends ESTestCase {
     }
 
     public void testDuplicateParts() throws Exception {
-        assumeFalse("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
         parseAndExpectFailure("{\n" +
                 "  \"ping\": {" +
                 "    \"documentation\": \"http://www.elasticsearch.org/guide/\"," +
@@ -106,8 +107,8 @@ public class ClientYamlSuiteRestApiParserFailingTests extends ESTestCase {
     }
 
     public void testDuplicateParams() throws Exception {
-        assumeFalse("Test only makes sense if JSON parser doesn't have strict duplicate checks enabled",
-            JsonXContent.isStrictDuplicateDetectionEnabled());
+        assumeFalse("Test only makes sense if XContent parser doesn't have strict duplicate checks enabled",
+            XContent.isStrictDuplicateDetectionEnabled());
         parseAndExpectFailure("{\n" +
                 "  \"ping\": {" +
                 "    \"documentation\": \"http://www.elasticsearch.org/guide/\"," +