diff --git a/src/MongoDB/ReadConcern.c b/src/MongoDB/ReadConcern.c
index 0faf04a1f..e14c85433 100644
--- a/src/MongoDB/ReadConcern.c
+++ b/src/MongoDB/ReadConcern.c
@@ -79,6 +79,23 @@ static PHP_METHOD(ReadConcern, getLevel)
 	RETURN_NULL();
 } /* }}} */
 
+/* {{{ proto boolean MongoDB\Driver\ReadConcern::isDefault()
+   Returns whether the read concern has not been modified (i.e. constructed
+   without a level or from a Manager with no read concern URI options). */
+static PHP_METHOD(ReadConcern, isDefault)
+{
+	php_phongo_readconcern_t *intern;
+	SUPPRESS_UNUSED_WARNING(return_value_ptr) SUPPRESS_UNUSED_WARNING(return_value_used)
+
+	intern = Z_READCONCERN_OBJ_P(getThis());
+
+	if (zend_parse_parameters_none() == FAILURE) {
+		return;
+	}
+
+	RETURN_BOOL(mongoc_read_concern_is_default(intern->read_concern));
+} /* }}} */
+
 /* {{{ proto array MongoDB\Driver\ReadConcern::bsonSerialize()
 */
 static PHP_METHOD(ReadConcern, bsonSerialize)
@@ -104,6 +121,7 @@ ZEND_END_ARG_INFO()
 static zend_function_entry php_phongo_readconcern_me[] = {
 	PHP_ME(ReadConcern, __construct, ai_ReadConcern___construct, ZEND_ACC_PUBLIC|ZEND_ACC_FINAL)
 	PHP_ME(ReadConcern, getLevel, ai_ReadConcern_void, ZEND_ACC_PUBLIC|ZEND_ACC_FINAL)
+	PHP_ME(ReadConcern, isDefault, ai_ReadConcern_void, ZEND_ACC_PUBLIC|ZEND_ACC_FINAL)
 	PHP_ME(ReadConcern, bsonSerialize, ai_ReadConcern_void, ZEND_ACC_PUBLIC|ZEND_ACC_FINAL)
 	PHP_FE_END
 };
diff --git a/src/MongoDB/WriteConcern.c b/src/MongoDB/WriteConcern.c
index 746eac016..730d37076 100644
--- a/src/MongoDB/WriteConcern.c
+++ b/src/MongoDB/WriteConcern.c
@@ -158,6 +158,23 @@ static PHP_METHOD(WriteConcern, getJournal)
 	RETURN_NULL();
 } /* }}} */
 
+/* {{{ proto boolean MongoDB\Driver\WriteConcern::isDefault()
+   Returns whether the write concern has not been modified (i.e. from a Manager
+   with no write concern URI options). */
+static PHP_METHOD(WriteConcern, isDefault)
+{
+	php_phongo_writeconcern_t *intern;
+	SUPPRESS_UNUSED_WARNING(return_value_ptr) SUPPRESS_UNUSED_WARNING(return_value_used)
+
+	intern = Z_WRITECONCERN_OBJ_P(getThis());
+
+	if (zend_parse_parameters_none() == FAILURE) {
+		return;
+	}
+
+	RETURN_BOOL(mongoc_write_concern_is_default(intern->write_concern));
+} /* }}} */
+
 /* {{{ proto array MongoDB\Driver\WriteConcern::bsonSerialize()
 */
 static PHP_METHOD(WriteConcern, bsonSerialize)
@@ -187,6 +204,7 @@ static zend_function_entry php_phongo_writeconcern_me[] = {
 	PHP_ME(WriteConcern, getW, ai_WriteConcern_void, ZEND_ACC_PUBLIC|ZEND_ACC_FINAL)
 	PHP_ME(WriteConcern, getWtimeout, ai_WriteConcern_void, ZEND_ACC_PUBLIC|ZEND_ACC_FINAL)
 	PHP_ME(WriteConcern, getJournal, ai_WriteConcern_void, ZEND_ACC_PUBLIC|ZEND_ACC_FINAL)
+	PHP_ME(WriteConcern, isDefault, ai_WriteConcern_void, ZEND_ACC_PUBLIC|ZEND_ACC_FINAL)
 	PHP_ME(WriteConcern, bsonSerialize, ai_WriteConcern_void, ZEND_ACC_PUBLIC|ZEND_ACC_FINAL)
 	PHP_FE_END
 };
diff --git a/src/libmongoc b/src/libmongoc
index 9d1873fa8..8f7ac9829 160000
--- a/src/libmongoc
+++ b/src/libmongoc
@@ -1 +1 @@
-Subproject commit 9d1873fa87a4b6b4a11db30a44eebd35891532c6
+Subproject commit 8f7ac98294ecb22d244e29f7b9fab3997d1caf31
diff --git a/tests/readConcern/readconcern-isdefault-001.phpt b/tests/readConcern/readconcern-isdefault-001.phpt
new file mode 100644
index 000000000..a63346ab4
--- /dev/null
+++ b/tests/readConcern/readconcern-isdefault-001.phpt
@@ -0,0 +1,38 @@
+--TEST--
+MongoDB\Driver\ReadConcern::isDefault()
+--SKIPIF--
+<?php require __DIR__ . "/../utils/basic-skipif.inc"?>
+--FILE--
+<?php
+require_once __DIR__ . "/../utils/basic.inc";
+
+$tests = array(
+    new MongoDB\Driver\ReadConcern(),
+    new MongoDB\Driver\ReadConcern(null),
+    new MongoDB\Driver\ReadConcern(MongoDB\Driver\ReadConcern::LOCAL),
+    new MongoDB\Driver\ReadConcern(MongoDB\Driver\ReadConcern::MAJORITY),
+    new MongoDB\Driver\ReadConcern('not-yet-supported'),
+    (new MongoDB\Driver\Manager('mongodb://127.0.0.1/?readconcernlevel=local'))->getReadConcern(),
+    (new MongoDB\Driver\Manager(null, ['readconcernlevel' => 'local']))->getReadConcern(),
+    (new MongoDB\Driver\Manager(null, ['readconcernlevel' => '']))->getReadConcern(),
+    (new MongoDB\Driver\Manager)->getReadConcern(),
+);
+
+foreach ($tests as $rc) {
+    var_dump($rc->isDefault());
+}
+
+?>
+===DONE===
+<?php exit(0); ?>
+--EXPECT--
+bool(true)
+bool(true)
+bool(false)
+bool(false)
+bool(false)
+bool(false)
+bool(false)
+bool(false)
+bool(true)
+===DONE===
diff --git a/tests/writeConcern/writeconcern-isdefault-001.phpt b/tests/writeConcern/writeconcern-isdefault-001.phpt
new file mode 100644
index 000000000..96c433478
--- /dev/null
+++ b/tests/writeConcern/writeconcern-isdefault-001.phpt
@@ -0,0 +1,28 @@
+--TEST--
+MongoDB\Driver\WriteConcern::isDefault()
+--SKIPIF--
+<?php require __DIR__ . "/../utils/basic-skipif.inc"?>
+--FILE--
+<?php
+require_once __DIR__ . "/../utils/basic.inc";
+
+$tests = array(
+    new MongoDB\Driver\WriteConcern(1),
+    (new MongoDB\Driver\Manager('mongodb://127.0.0.1/?w=1'))->getWriteConcern(),
+    (new MongoDB\Driver\Manager(null, ['w' => 1]))->getWriteConcern(),
+    (new MongoDB\Driver\Manager)->getWriteConcern(),
+);
+
+foreach ($tests as $wc) {
+    var_dump($wc->isDefault());
+}
+
+?>
+===DONE===
+<?php exit(0); ?>
+--EXPECT--
+bool(false)
+bool(false)
+bool(false)
+bool(true)
+===DONE===