diff --git a/hapi-fhir-base/src/main/java/ca/uhn/fhir/parser/JsonParser.java b/hapi-fhir-base/src/main/java/ca/uhn/fhir/parser/JsonParser.java
index 02f92d8e9f8..9ec3df3310b 100644
--- a/hapi-fhir-base/src/main/java/ca/uhn/fhir/parser/JsonParser.java
+++ b/hapi-fhir-base/src/main/java/ca/uhn/fhir/parser/JsonParser.java
@@ -734,6 +734,9 @@ public class JsonParser extends BaseParser implements IJsonLikeParser {
 		beginArray(theEventWriter, arrayName);
 		for (Map.Entry<ResourceMetadataKeyEnum<?>, Object> key : extensions) {
 			ExtensionDt extension = (ExtensionDt) key.getValue();
+			if (!extension.getAllUndeclaredExtensions().isEmpty()) {
+				throw new IllegalArgumentException("Sub-extensions on metadata isn't supported");
+			}
 			theEventWriter.beginObject();
 			writeOptionalTagWithTextNode(theEventWriter, "url", extension.getUrl());
 			String extensionDatatype = myContext.getRuntimeChildUndeclaredExtensionDefinition().getChildNameByDatatype(extension.getValue().getClass());
diff --git a/hapi-fhir-structures-dstu2/src/test/java/ca/uhn/fhir/parser/JsonParserDstu2Test.java b/hapi-fhir-structures-dstu2/src/test/java/ca/uhn/fhir/parser/JsonParserDstu2Test.java
index dca45aaffa9..266321bda1a 100644
--- a/hapi-fhir-structures-dstu2/src/test/java/ca/uhn/fhir/parser/JsonParserDstu2Test.java
+++ b/hapi-fhir-structures-dstu2/src/test/java/ca/uhn/fhir/parser/JsonParserDstu2Test.java
@@ -1745,6 +1745,17 @@ public class JsonParserDstu2Test {
 		// @formatter:on
 	}
 
+	@Test(expected = IllegalArgumentException.class)
+	public void testCannotEncodeSubextensionsOnMeta() {
+		ProcedureRequest procedureRequest = new ProcedureRequest();
+		procedureRequest.setStatus(ProcedureRequestStatusEnum.ACCEPTED);
+		ExtensionDt parent = new ExtensionDt(false, "#parent");
+		parent.addUndeclaredExtension(new ExtensionDt(false, "#child", new DurationDt().setValue(123)));
+		procedureRequest.getResourceMetadata().put(new ResourceMetadataKeyEnum.ExtensionResourceMetadataKey(parent.getUrl()), parent);
+
+		String json = ourCtx.newJsonParser().setPrettyPrint(true).encodeResourceToString(procedureRequest);
+	}
+
 	private void addExtensionResourceMetadataKeyToResource(BaseResource resource, boolean isModifier, String url, String value) {
 		ExtensionDt extensionDt = new ExtensionDt(isModifier, url, new StringDt(value));
 		resource.getResourceMetadata()