diff --git a/conformance/binary_json_conformance_suite.cc b/conformance/binary_json_conformance_suite.cc
index 6951cca0a86c..cf29d133eaf1 100644
--- a/conformance/binary_json_conformance_suite.cc
+++ b/conformance/binary_json_conformance_suite.cc
@@ -1766,6 +1766,7 @@ void BinaryAndJsonConformanceSuite::RunJsonTests() {
   RunJsonTestsForStruct();
   RunJsonTestsForValue();
   RunJsonTestsForAny();
+  RunJsonTestsForUnknownEnumStringValues();
 
   RunValidJsonIgnoreUnknownTest("IgnoreUnknownJsonNumber", REQUIRED,
                                 R"({
@@ -1801,6 +1802,43 @@ void BinaryAndJsonConformanceSuite::RunJsonTests() {
   ExpectParseFailureForJson("RejectTopLevelNull", REQUIRED, "null");
 }
 
+void BinaryAndJsonConformanceSuite::RunJsonTestsForUnknownEnumStringValues() {
+  // Tests the handling of unknown enum values when encoded as string labels.
+  // The expected behavior depends on whether unknown fields are ignored:
+  // * when ignored, the parser should ignore the unknown enum string value.
+  // * when not ignored, the parser should fail.
+  struct TestCase {
+    // Used in the test name.
+    string enum_location;
+    // JSON input which will contain the unknown field.
+    string input_json;
+  };
+  const std::vector<TestCase> test_cases = {
+    {"InOptionalField", R"json({
+      "optional_nested_enum": "UNKNOWN_ENUM_VALUE"
+    })json"},
+    {"InRepeatedField", R"json({
+      "repeated_nested_enum": ["UNKNOWN_ENUM_VALUE"]
+    })json"},
+    {"InMapValue", R"json({
+      "map_string_nested_enum": {"key": "UNKNOWN_ENUM_VALUE"}
+    })json"},
+  };
+  for (const TestCase& test_case : test_cases) {
+    // Unknown enum string value is a parse failure when not ignoring unknown fields.
+    ExpectParseFailureForJson(
+        absl::StrCat("RejectUnknownEnumStringValue", test_case.enum_location),
+        RECOMMENDED,
+        test_case.input_json);
+    // Unknown enum string value is ignored when ignoring unknown fields.
+    RunValidJsonIgnoreUnknownTest(
+        absl::StrCat("IgnoreUnknownEnumStringValue", test_case.enum_location),
+        RECOMMENDED,
+        test_case.input_json,
+        "");
+  }
+}
+
 void BinaryAndJsonConformanceSuite::RunJsonTestsForFieldNameConvention() {
   RunValidJsonTest(
       "FieldNameInSnakeCase", REQUIRED,
diff --git a/conformance/binary_json_conformance_suite.h b/conformance/binary_json_conformance_suite.h
index e45a92f89f95..b859921a37f4 100644
--- a/conformance/binary_json_conformance_suite.h
+++ b/conformance/binary_json_conformance_suite.h
@@ -56,6 +56,7 @@ class BinaryAndJsonConformanceSuite : public ConformanceTestSuite {
   void RunJsonTestsForStruct();
   void RunJsonTestsForValue();
   void RunJsonTestsForAny();
+  void RunJsonTestsForUnknownEnumStringValues();
   void RunValidJsonTest(const std::string& test_name, ConformanceLevel level,
                         const std::string& input_json,
                         const std::string& equivalent_text_format);
diff --git a/conformance/failure_list_cpp.txt b/conformance/failure_list_cpp.txt
index a68602cee968..5af3dfc30082 100644
--- a/conformance/failure_list_cpp.txt
+++ b/conformance/failure_list_cpp.txt
@@ -17,6 +17,8 @@ Recommended.Proto3.JsonInput.FieldNameDuplicate
 Recommended.Proto3.JsonInput.FieldNameDuplicateDifferentCasing1
 Recommended.Proto3.JsonInput.FieldNameDuplicateDifferentCasing2
 Recommended.Proto3.JsonInput.FieldNameNotQuoted
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapValue.ProtobufOutput
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedField.ProtobufOutput
 Recommended.Proto3.JsonInput.MapFieldValueIsNull
 Recommended.Proto3.JsonInput.RepeatedFieldMessageElementIsNull
 Recommended.Proto3.JsonInput.RepeatedFieldPrimitiveElementIsNull
diff --git a/conformance/failure_list_php.txt b/conformance/failure_list_php.txt
index 3232047aa759..4876e10ba47a 100644
--- a/conformance/failure_list_php.txt
+++ b/conformance/failure_list_php.txt
@@ -5,6 +5,8 @@ Recommended.Proto2.JsonInput.FieldNameExtension.Validator
 Recommended.Proto3.JsonInput.BytesFieldBase64Url.JsonOutput
 Recommended.Proto3.JsonInput.BytesFieldBase64Url.ProtobufOutput
 Recommended.Proto3.JsonInput.FieldMaskInvalidCharacter
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapValue.ProtobufOutput
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedField.ProtobufOutput
 Recommended.Proto3.ProtobufInput.ValidDataOneofBinary.MESSAGE.Merge.ProtobufOutput
 Required.Proto2.JsonInput.StoresDefaultPrimitive.Validator
 Required.Proto3.JsonInput.DoubleFieldTooSmall
diff --git a/conformance/failure_list_php_c.txt b/conformance/failure_list_php_c.txt
index 63c7e8a024cc..284448652f6f 100644
--- a/conformance/failure_list_php_c.txt
+++ b/conformance/failure_list_php_c.txt
@@ -1,2 +1,4 @@
 Recommended.Proto2.JsonInput.FieldNameExtension.Validator
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapValue.ProtobufOutput
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedField.ProtobufOutput
 Required.Proto2.JsonInput.StoresDefaultPrimitive.Validator
diff --git a/conformance/failure_list_python.txt b/conformance/failure_list_python.txt
index e69de29bb2d1..8bbf094293d4 100644
--- a/conformance/failure_list_python.txt
+++ b/conformance/failure_list_python.txt
@@ -0,0 +1,3 @@
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapValue.ProtobufOutput
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInOptionalField.ProtobufOutput
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedField.ProtobufOutput
diff --git a/conformance/failure_list_python_cpp.txt b/conformance/failure_list_python_cpp.txt
index 9efb6cf8b77b..de84bd3b0e9a 100644
--- a/conformance/failure_list_python_cpp.txt
+++ b/conformance/failure_list_python_cpp.txt
@@ -6,3 +6,6 @@
 #
 # TODO(haberman): insert links to corresponding bugs tracking the issue.
 # Should we use GitHub issues or the Google-internal bug tracker?
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapValue.ProtobufOutput
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInOptionalField.ProtobufOutput
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedField.ProtobufOutput
diff --git a/conformance/failure_list_ruby.txt b/conformance/failure_list_ruby.txt
index 4938202ad70b..3c744391cf75 100644
--- a/conformance/failure_list_ruby.txt
+++ b/conformance/failure_list_ruby.txt
@@ -27,6 +27,8 @@ Recommended.Proto2.ProtobufInput.ValidDataRepeated.UINT32.PackedInput.PackedOutp
 Recommended.Proto2.ProtobufInput.ValidDataRepeated.UINT32.UnpackedInput.PackedOutput.ProtobufOutput
 Recommended.Proto2.ProtobufInput.ValidDataRepeated.UINT64.PackedInput.PackedOutput.ProtobufOutput
 Recommended.Proto2.ProtobufInput.ValidDataRepeated.UINT64.UnpackedInput.PackedOutput.ProtobufOutput
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapValue.ProtobufOutput
+Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedField.ProtobufOutput
 Recommended.Proto3.ProtobufInput.ValidDataOneofBinary.MESSAGE.Merge.ProtobufOutput
 Recommended.Proto3.ProtobufInput.ValidDataRepeated.BOOL.PackedInput.UnpackedOutput.ProtobufOutput
 Recommended.Proto3.ProtobufInput.ValidDataRepeated.BOOL.UnpackedInput.UnpackedOutput.ProtobufOutput