diff --git a/CHANGES.rst b/CHANGES.rst
index c874177..a5ae7da 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -8,7 +8,8 @@ Here you can see the full list of changes between each SQLAlchemy-Utils release.
 ^^^^^^^^^^^^^^^^^^^
 
 - Added Asterisk compiler
-- Added row_to_json FunctionElement
+- Added row_to_json GenericFunction
+- Added array_agg GenericFunction
 - Made quote function accept dialect object as the first paremeter
 - Made has_index work with tables without primary keys (#148)
 
diff --git a/sqlalchemy_utils/__init__.py b/sqlalchemy_utils/__init__.py
index bdbfb46..8b85372 100644
--- a/sqlalchemy_utils/__init__.py
+++ b/sqlalchemy_utils/__init__.py
@@ -8,7 +8,7 @@ from .asserts import (  # noqa
 )
 from .exceptions import ImproperlyConfigured  # noqa
 from .expression_parser import ExpressionParser  # noqa
-from .expressions import Asterisk, row_to_json # noqa
+from .expressions import array_agg, Asterisk, row_to_json # noqa
 from .functions import (  # noqa
     analyze,
     create_database,
diff --git a/sqlalchemy_utils/expressions.py b/sqlalchemy_utils/expressions.py
index c0f5fcf..12a6bcd 100644
--- a/sqlalchemy_utils/expressions.py
+++ b/sqlalchemy_utils/expressions.py
@@ -1,5 +1,5 @@
 import sqlalchemy as sa
-from sqlalchemy.dialects.postgresql import JSON
+from sqlalchemy.dialects.postgresql import ARRAY, JSON
 from sqlalchemy.ext.compiler import compiles
 from sqlalchemy.sql.elements import ColumnClause
 from sqlalchemy.sql.expression import (
@@ -9,6 +9,7 @@ from sqlalchemy.sql.expression import (
     Executable,
     FunctionElement
 )
+from sqlalchemy.sql.functions import GenericFunction
 
 from sqlalchemy_utils.functions.orm import quote
 
@@ -92,7 +93,7 @@ def compile_array_get(element, compiler, **kw):
     )
 
 
-class row_to_json(FunctionElement):
+class row_to_json(GenericFunction):
     name = 'row_to_json'
     type = JSON
 
@@ -102,6 +103,30 @@ def compile_row_to_json(element, compiler, **kw):
     return "%s(%s)" % (element.name, compiler.process(element.clauses))
 
 
+class json_array_length(GenericFunction):
+    name = 'json_array_length'
+    type = sa.Integer
+
+
+@compiles(json_array_length, 'postgresql')
+def compile_json_array_length(element, compiler, **kw):
+    return "%s(%s)" % (element.name, compiler.process(element.clauses))
+
+
+class array_agg(GenericFunction):
+    name = 'array_agg'
+    type = ARRAY
+
+    def __init__(self, arg, **kw):
+        self.type = ARRAY(arg.type)
+        GenericFunction.__init__(self, arg, **kw)
+
+
+@compiles(array_agg, 'postgresql')
+def compile_json_array_length(element, compiler, **kw):
+    return "%s(%s)" % (element.name, compiler.process(element.clauses))
+
+
 class Asterisk(ColumnElement):
     def __init__(self, selectable):
         self.selectable = selectable
diff --git a/tests/test_expressions.py b/tests/test_expressions.py
index d73ad02..b6de6b6 100644
--- a/tests/test_expressions.py
+++ b/tests/test_expressions.py
@@ -2,7 +2,7 @@ import sqlalchemy as sa
 from pytest import raises
 from sqlalchemy.dialects import postgresql
 
-from sqlalchemy_utils import Asterisk, row_to_json
+from sqlalchemy_utils import array_agg, Asterisk, row_to_json
 from sqlalchemy_utils.expressions import explain, explain_analyze
 from tests import TestCase
 
@@ -112,16 +112,32 @@ class TestAsterisk(object):
 class TestRowToJson(object):
     def test_compiler_with_default_dialect(self):
         with raises(sa.exc.CompileError):
-            assert str(row_to_json(sa.text('article.*'))) == (
-                'row_to_json(article.*)'
-            )
+            str(row_to_json(sa.text('article.*')))
 
     def test_compiler_with_postgresql(self):
         assert str(row_to_json(sa.text('article.*')).compile(
             dialect=postgresql.dialect()
-        )) == (
-            'row_to_json(article.*)'
-        )
+        )) == 'row_to_json(article.*)'
 
     def test_type(self):
-        assert row_to_json(sa.text('article.*')).type == postgresql.JSON
+        assert isinstance(
+            sa.func.row_to_json(sa.text('article.*')).type,
+            postgresql.JSON
+        )
+
+
+class TestArrayAgg(object):
+    def test_compiler_with_default_dialect(self):
+        with raises(sa.exc.CompileError):
+            str(array_agg(sa.text('u.name')))
+
+    def test_compiler_with_postgresql(self):
+        assert str(array_agg(sa.text('u.name')).compile(
+            dialect=postgresql.dialect()
+        )) == "array_agg(u.name)"
+
+    def test_type(self):
+        assert isinstance(
+            sa.func.array_agg(sa.text('u.name')).type,
+            postgresql.ARRAY
+        )