diff --git a/jerry-core/ecma/operations/ecma-objects.c b/jerry-core/ecma/operations/ecma-objects.c
index 76daa04348..cc1b0e3b5c 100644
--- a/jerry-core/ecma/operations/ecma-objects.c
+++ b/jerry-core/ecma/operations/ecma-objects.c
@@ -2041,7 +2041,37 @@ ecma_op_object_get_property_names (ecma_object_t *obj_p, /**< object */
 #if ENABLED (JERRY_ES2015_BUILTIN_PROXY)
   if (ECMA_OBJECT_IS_PROXY (obj_p))
   {
-    return ecma_proxy_object_own_property_keys (obj_p);
+    /* Integrated a part of ECMA 262 v6 7.3.21 EnumerableOwnNames operation. */
+    ecma_collection_t *proxy_keys = ecma_proxy_object_own_property_keys (obj_p);
+    if (JERRY_UNLIKELY (proxy_keys == NULL))
+    {
+      return proxy_keys;
+    }
+    ecma_collection_t *return_keys = ecma_new_collection ();
+
+    /* Move valid elements to the output collection */
+    for (uint32_t i = 0; i < proxy_keys->item_count; i++)
+    {
+      ecma_value_t entry = proxy_keys->buffer_p[i];
+      ecma_string_t *prop_name_p = ecma_get_prop_name_from_value (entry);
+      bool prop_is_symbol = ecma_prop_name_is_symbol (prop_name_p);
+
+      if (prop_is_symbol && ((opts & (ECMA_LIST_SYMBOLS | ECMA_LIST_SYMBOLS_ONLY)) != 0))
+      {
+        ecma_collection_push_back (return_keys, entry);
+      }
+      else if (!prop_is_symbol && (opts & ECMA_LIST_SYMBOLS_ONLY) == 0)
+      {
+        ecma_collection_push_back (return_keys, entry);
+      }
+      else
+      {
+        ecma_free_value (entry);
+      }
+    }
+
+    ecma_collection_destroy (proxy_keys);
+    return return_keys;
   }
 #endif /* ENABLED (JERRY_ES2015_BUILTIN_PROXY) */
 
diff --git a/tests/jerry/es2015/proxy_own_keys.js b/tests/jerry/es2015/proxy_own_keys.js
index 5cc79be171..9c2f038043 100644
--- a/tests/jerry/es2015/proxy_own_keys.js
+++ b/tests/jerry/es2015/proxy_own_keys.js
@@ -16,6 +16,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+function array_check(result_array, expected_array) {
+  assert(result_array instanceof Array);
+  assert(result_array.length === expected_array.length);
+  for (var idx = 0; idx < expected_array.length; idx++) {
+    assert(result_array[idx] === expected_array[idx]);
+  }
+}
+
 var target = {};
 var handler = { ownKeys (target) {
   throw 42;
@@ -56,26 +64,29 @@ try {
 }
 
 // test basic functionality
+var symA = Symbol("smA");
+var symB = Symbol("smB");
 var target = { prop1: "prop1", prop2: "prop2"};
+target[symB] = "s3";
 var handler = {
   ownKeys: function(target) {
-    return ["foo", "bar"];
+    return ["foo", "bar", symA];
   }
 }
 
 var proxy = new Proxy(target, handler);
 
-assert(JSON.stringify(Reflect.ownKeys(proxy)) === '["foo","bar"]');
-assert(JSON.stringify(Object.getOwnPropertyNames(proxy)) === '["foo","bar"]');
-assert(JSON.stringify(Object.keys(proxy)) === '["foo","bar"]');
-assert(JSON.stringify(Object.getOwnPropertySymbols(proxy)) === '["foo","bar"]');
+array_check(Reflect.ownKeys(proxy), ["foo", "bar", symA]);
+array_check(Object.getOwnPropertyNames(proxy), ["foo", "bar"]);
+array_check(Object.keys(proxy), ["foo", "bar"]);
+array_check(Object.getOwnPropertySymbols(proxy), [symA]);
 
 handler.ownKeys = function(target) {return Object.getOwnPropertyNames(target);};
 
-assert(JSON.stringify(Reflect.ownKeys(proxy)) === '["prop1","prop2"]');
-assert(JSON.stringify(Object.getOwnPropertyNames(proxy)) === '["prop1","prop2"]');
-assert(JSON.stringify(Object.keys(proxy)) === '["prop1","prop2"]');
-assert(JSON.stringify(Object.getOwnPropertySymbols(proxy)) === '["prop1","prop2"]');
+array_check(Reflect.ownKeys(proxy), ["prop1", "prop2"]);
+array_check(Object.getOwnPropertyNames(proxy), ["prop1", "prop2"]);
+array_check(Object.keys(proxy), ["prop1", "prop2"]);
+array_check(Object.getOwnPropertySymbols(proxy), []);
 
 // test with no trap
 var target = { prop1: "prop1", prop2: "prop2"};
diff --git a/tests/jerry/es2015/regression-test-issue-3787.js b/tests/jerry/es2015/regression-test-issue-3787.js
new file mode 100644
index 0000000000..40a4a0394f
--- /dev/null
+++ b/tests/jerry/es2015/regression-test-issue-3787.js
@@ -0,0 +1,22 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+var symbol = Symbol("s");
+var obj = {demo: "3"};
+obj[symbol] = 3;
+
+var proxy = new Proxy(obj, []);
+var str = JSON.stringify(proxy);
+
+assert(str === '{"demo":"3"}');