diff --git a/src/Message/Post/PostBody.php b/src/Message/Post/PostBody.php
index 47b8235d..d587365f 100644
--- a/src/Message/Post/PostBody.php
+++ b/src/Message/Post/PostBody.php
@@ -5,8 +5,6 @@ namespace GuzzleHttp\Message\Post;
 use GuzzleHttp\Message\RequestInterface;
 use GuzzleHttp\Stream\Stream;
 use GuzzleHttp\Stream\StreamInterface;
-use GuzzleHttp\QueryAggregator\PhpAggregator;
-use GuzzleHttp\QueryAggregator\QueryAggregatorInterface;
 use GuzzleHttp\Query;
 
 /**
@@ -17,7 +15,7 @@ class PostBody implements PostBodyInterface
     /** @var StreamInterface */
     private $body;
 
-    /** @var QueryAggregatorInterface */
+    /** @var callable */
     private $aggregator;
 
     private $fields = [];
@@ -57,11 +55,15 @@ class PostBody implements PostBodyInterface
     }
 
     /**
-     * Set the aggregation strategy that will be used to turn multi-valued fields into a string
+     * Set the aggregation strategy that will be used to turn multi-valued
+     * fields into a string.
      *
-     * @param QueryAggregatorInterface $aggregator
+     * The aggregation function accepts a deeply nested array of query string
+     * values and returns a flattened associative array of key value pairs.
+     *
+     * @param callable $aggregator
      */
-    final public function setAggregator(QueryAggregatorInterface $aggregator)
+    final public function setAggregator(callable $aggregator)
     {
         $this->aggregator = $aggregator;
     }
@@ -224,12 +226,12 @@ class PostBody implements PostBodyInterface
     /**
      * Get the aggregator used to join multi-valued field parameters
      *
-     * @return QueryAggregatorInterface
+     * @return callable
      */
     final protected function getAggregator()
     {
         if (!$this->aggregator) {
-            $this->aggregator = new PhpAggregator();
+            $this->aggregator = Query::phpAggregator();
         }
 
         return $this->aggregator;
diff --git a/src/Query.php b/src/Query.php
index b5fd763d..09a910c9 100644
--- a/src/Query.php
+++ b/src/Query.php
@@ -2,10 +2,6 @@
 
 namespace GuzzleHttp;
 
-use GuzzleHttp\QueryAggregator\QueryAggregatorInterface;
-use GuzzleHttp\QueryAggregator\DuplicateAggregator;
-use GuzzleHttp\QueryAggregator\PhpAggregator;
-
 /**
  * Manages query string variables and can aggregate them into a string
  */
@@ -17,7 +13,7 @@ class Query extends Collection
     /** @var bool URL encode fields and values */
     private $encoding = self::RFC3986;
 
-    /** @var QueryAggregatorInterface */
+    /** @var callable */
     private $aggregator;
 
     /**
@@ -60,7 +56,7 @@ class Query extends Collection
 
         // Use the duplicate aggregator if duplicates were found and not using PHP style arrays
         if ($foundDuplicates && !$foundPhpStyle) {
-            $q->setAggregator(new DuplicateAggregator());
+            $q->setAggregator(self::duplicateAggregator());
         }
 
         return $q;
@@ -77,12 +73,20 @@ class Query extends Collection
             return '';
         }
 
+        // The default aggregator is statically cached
+        static $defaultAggregator;
+
         if (!$this->aggregator) {
-            $this->aggregator = new PhpAggregator();
+            if (!$defaultAggregator) {
+                $defaultAggregator = self::phpAggregator();
+            }
+            $this->aggregator = $defaultAggregator;
         }
 
         $result = '';
-        foreach ($this->aggregator->aggregate($this->data) as $key => $values) {
+        $aggregator = $this->aggregator;
+
+        foreach ($aggregator($this->data) as $key => $values) {
             foreach ($values as $value) {
                 if ($result) {
                     $result .= '&';
@@ -110,13 +114,20 @@ class Query extends Collection
     }
 
     /**
-     * Controls how multi-valued query string parameters are aggregated into a string
+     * Controls how multi-valued query string parameters are aggregated into a
+     * string.
      *
-     * @param QueryAggregatorInterface $aggregator Converts an array of query string variables into a string
+     *     $query->setAggregator($query::duplicateAggregator());
+     *
+     * @param callable $aggregator Callable used to converts a deeply nested
+     *     array of query string variables into a flattened array of key value
+     *     pairs. The callable accepts an array of query data and returns a
+     *     flattened array of key value pairs where each value is an array of
+     *     strings.
      *
      * @return self
      */
-    public function setAggregator(QueryAggregatorInterface $aggregator)
+    public function setAggregator(callable $aggregator)
     {
         $this->aggregator = $aggregator;
 
@@ -141,4 +152,74 @@ class Query extends Collection
 
         return $this;
     }
+
+    /**
+     * Query string aggregator that does not aggregate nested query string
+     * values and allows duplicates in the resulting array.
+     *
+     * Example: http://test.com?q=1&q=2
+     *
+     * @return callable
+     */
+    public static function duplicateAggregator()
+    {
+        return function (array $data) {
+            return self::walkQuery($data, '', function ($key, $prefix) {
+                return is_int($key) ? $prefix : "{$prefix}[{$key}]";
+            });
+        };
+    }
+
+    /**
+     * Aggregates nested query string variables using the same techinque as
+     * ``http_build_query()``.
+     *
+     * @param bool $numericIndices Pass false to not include numeric indices
+     *     when multi-values query string parameters are present.
+     *
+     * @return callable
+     */
+    public static function phpAggregator($numericIndices = true)
+    {
+        return function (array $data) use ($numericIndices) {
+            return self::walkQuery(
+                $data,
+                '',
+                function ($key, $prefix) use ($numericIndices) {
+                    return !$numericIndices && is_int($key)
+                        ? "{$prefix}[]"
+                        : "{$prefix}[{$key}]";
+                }
+            );
+        };
+    }
+
+    /**
+     * Easily create query aggregation functions by providing a key prefix
+     * function to this query string array walker.
+     *
+     * @param array    $query     Query string to walk
+     * @param string   $keyPrefix Key prefix (start with '')
+     * @param callable $prefixer  Function used to create a key prefix
+     *
+     * @return array
+     */
+    public static function walkQuery(array $query, $keyPrefix, callable $prefixer)
+    {
+        $result = [];
+        foreach ($query as $key => $value) {
+            if ($keyPrefix) {
+                $key = $prefixer($key, $keyPrefix);
+            }
+            if (is_array($value)) {
+                $result += self::walkQuery($value, $key, $prefixer);
+            } elseif (isset($result[$key])) {
+                $result[$key][] = $value;
+            } else {
+                $result[$key] = array($value);
+            }
+        }
+
+        return $result;
+    }
 }
diff --git a/src/QueryAggregator/AbstractAggregator.php b/src/QueryAggregator/AbstractAggregator.php
deleted file mode 100644
index 2344ef14..00000000
--- a/src/QueryAggregator/AbstractAggregator.php
+++ /dev/null
@@ -1,40 +0,0 @@
-<?php
-
-namespace GuzzleHttp\QueryAggregator;
-
-abstract class AbstractAggregator implements QueryAggregatorInterface
-{
-    public function aggregate(array $query)
-    {
-        return $this->walkQuery($query, '');
-    }
-
-    protected function walkQuery(array $query, $keyPrefix)
-    {
-        $result = [];
-        foreach ($query as $key => $value) {
-            if ($keyPrefix) {
-                $key = $this->createPrefixKey($key, $keyPrefix);
-            }
-            if (is_array($value)) {
-                $result += $this->walkQuery($value, $key);
-            } elseif (isset($result[$key])) {
-                $result[$key][] = $value;
-            } else {
-                $result[$key] = array($value);
-            }
-        }
-
-        return $result;
-    }
-
-    /**
-     * Computes a key for a key and prefix
-     *
-     * @param string $key
-     * @param string $keyPrefix
-     *
-     * @return string
-     */
-    abstract protected function createPrefixKey($key, $keyPrefix);
-}
diff --git a/src/QueryAggregator/DuplicateAggregator.php b/src/QueryAggregator/DuplicateAggregator.php
deleted file mode 100644
index 022cca1d..00000000
--- a/src/QueryAggregator/DuplicateAggregator.php
+++ /dev/null
@@ -1,15 +0,0 @@
-<?php
-
-namespace GuzzleHttp\QueryAggregator;
-
-/**
- * Aggregates nested query string variables using PHP style arrays, but does not
- * combine duplicate values of the same name under array keys.
- */
-class DuplicateAggregator extends AbstractAggregator
-{
-    protected function createPrefixKey($key, $keyPrefix)
-    {
-        return is_int($key) ? $keyPrefix : "{$keyPrefix}[{$key}]";
-    }
-}
diff --git a/src/QueryAggregator/PhpAggregator.php b/src/QueryAggregator/PhpAggregator.php
deleted file mode 100644
index fd78ec0e..00000000
--- a/src/QueryAggregator/PhpAggregator.php
+++ /dev/null
@@ -1,24 +0,0 @@
-<?php
-
-namespace GuzzleHttp\QueryAggregator;
-
-/**
- * Aggregates nested query string variables using PHP style []
- */
-class PhpAggregator extends AbstractAggregator
-{
-    private $numericIndices;
-
-    /**
-     * @param bool $numericIndices Set to false to disable numeric indices (e.g. foo[] = bar vs foo[0] = bar)
-     */
-    public function __construct($numericIndices = true)
-    {
-        $this->numericIndices = $numericIndices;
-    }
-
-    protected function createPrefixKey($key, $prefix)
-    {
-        return !$this->numericIndices && is_int($key) ? "{$prefix}[]" : "{$prefix}[{$key}]";
-    }
-}
diff --git a/src/QueryAggregator/QueryAggregatorInterface.php b/src/QueryAggregator/QueryAggregatorInterface.php
deleted file mode 100644
index 2b9b5d2e..00000000
--- a/src/QueryAggregator/QueryAggregatorInterface.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php
-
-namespace GuzzleHttp\QueryAggregator;
-
-/**
- * Interface used for aggregating multi-value query string parameters into a flattened array
- */
-interface QueryAggregatorInterface
-{
-    /**
-     * Aggregate a query string array into a flattened array
-     *
-     * @param array  $query Query string parameters
-     *
-     * @return array
-     */
-    public function aggregate(array $query);
-}
diff --git a/tests/Message/Post/PostBodyTest.php b/tests/Message/Post/PostBodyTest.php
index 1c50dac6..4d3497bd 100644
--- a/tests/Message/Post/PostBodyTest.php
+++ b/tests/Message/Post/PostBodyTest.php
@@ -5,7 +5,7 @@ namespace GuzzleHttp\Tests\Message\Post;
 use GuzzleHttp\Message\Post\PostBody;
 use GuzzleHttp\Message\Request;
 use GuzzleHttp\Message\Post\PostFile;
-use GuzzleHttp\QueryAggregator\DuplicateAggregator;
+use GuzzleHttp\Query;
 
 /**
  * @covers GuzzleHttp\Message\Post\PostBody
@@ -112,7 +112,7 @@ class PostBodyTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals('foo%5B0%5D=baz&foo%5B1%5D=bar', (string) $b);
         $b = new PostBody();
         $b->setField('foo', ['baz', 'bar']);
-        $agg = new DuplicateAggregator();
+        $agg = Query::duplicateAggregator();
         $b->setAggregator($agg);
         $this->assertEquals('foo=baz&foo=bar', (string) $b);
     }
diff --git a/tests/QueryAggregator/DuplicateAggregatorTest.php b/tests/QueryAggregator/DuplicateAggregatorTest.php
deleted file mode 100644
index 0a4a6ad3..00000000
--- a/tests/QueryAggregator/DuplicateAggregatorTest.php
+++ /dev/null
@@ -1,44 +0,0 @@
-<?php
-
-namespace GuzzleHttp\Tests\QueryAggregator;
-
-use GuzzleHttp\QueryAggregator\DuplicateAggregator;
-
-/**
- * @covers \GuzzleHttp\QueryAggregator\DuplicateAggregator
- * @covers \GuzzleHttp\QueryAggregator\AbstractAggregator
- */
-class DuplicateAggregatorTest extends \PHPUnit_Framework_TestCase
-{
-    private $encodeData = [
-        't' => [
-            'v1' => ['a', '1'],
-            'v2' => 'b',
-            'v3' => ['v4' => 'c', 'v5' => 'd']
-        ]
-    ];
-
-    public function testEncodes()
-    {
-        $agg = new DuplicateAggregator();
-        $result = $agg->aggregate($this->encodeData);
-        $this->assertEquals(array(
-            't[v1]' => ['a', '1'],
-            't[v2]' => ['b'],
-            't[v3][v4]' => ['c'],
-            't[v3][v5]' => ['d'],
-        ), $result);
-    }
-
-    public function testEncodesNoNumericIndices()
-    {
-        $agg = new DuplicateAggregator(false);
-        $result = $agg->aggregate($this->encodeData);
-        $this->assertEquals(array(
-            't[v1]' => ['a', '1'],
-            't[v2]' => ['b'],
-            't[v3][v4]' => ['c'],
-            't[v3][v5]' => ['d'],
-        ), $result);
-    }
-}
diff --git a/tests/QueryAggregator/PhpAggregatorTest.php b/tests/QueryAggregator/PhpAggregatorTest.php
deleted file mode 100644
index 0481f61b..00000000
--- a/tests/QueryAggregator/PhpAggregatorTest.php
+++ /dev/null
@@ -1,45 +0,0 @@
-<?php
-
-namespace GuzzleHttp\Tests\QueryAggregator;
-
-use GuzzleHttp\QueryAggregator\PhpAggregator;
-
-/**
- * @covers \GuzzleHttp\QueryAggregator\PhpAggregator
- * @covers \GuzzleHttp\QueryAggregator\AbstractAggregator
- */
-class PhpAggregatorTest extends \PHPUnit_Framework_TestCase
-{
-    private $encodeData = [
-        't' => [
-            'v1' => ['a', '1'],
-            'v2' => 'b',
-            'v3' => ['v4' => 'c', 'v5' => 'd']
-        ]
-    ];
-
-    public function testEncodes()
-    {
-        $agg = new PhpAggregator();
-        $result = $agg->aggregate($this->encodeData);
-        $this->assertEquals(array(
-            't[v1][0]' => ['a'],
-            't[v1][1]' => ['1'],
-            't[v2]' => ['b'],
-            't[v3][v4]' => ['c'],
-            't[v3][v5]' => ['d'],
-        ), $result);
-    }
-
-    public function testEncodesNoNumericIndices()
-    {
-        $agg = new PhpAggregator(false);
-        $result = $agg->aggregate($this->encodeData);
-        $this->assertEquals(array(
-            't[v1][]' => ['a', '1'],
-            't[v2]' => ['b'],
-            't[v3][v4]' => ['c'],
-            't[v3][v5]' => ['d'],
-        ), $result);
-    }
-}
diff --git a/tests/QueryTest.php b/tests/QueryTest.php
index 841db488..a5ca87b1 100644
--- a/tests/QueryTest.php
+++ b/tests/QueryTest.php
@@ -3,7 +3,6 @@
 namespace GuzzleHttp\Tests;
 
 use GuzzleHttp\Query;
-use GuzzleHttp\QueryAggregator\DuplicateAggregator;
 
 class QueryTest extends \PHPUnit_Framework_TestCase
 {
@@ -50,17 +49,10 @@ class QueryTest extends \PHPUnit_Framework_TestCase
 
     public function testCanSetAggregator()
     {
-        $agg = $this->getMockBuilder('GuzzleHttp\QueryAggregator\QueryAggregatorInterface')
-            ->setMethods('aggregate')
-            ->getMockForAbstractClass();
-
         $q = new Query(['foo' => ['bar', 'baz']]);
-        $q->setAggregator($agg);
-
-        $agg->expects($this->once())
-            ->method('aggregate')
-            ->will($this->returnValue(['foo' => ['barANDbaz']]));
-
+        $q->setAggregator(function (array $data) {
+            return ['foo' => ['barANDbaz']];
+        });
         $this->assertEquals('foo=barANDbaz', (string) $q);
     }
 
@@ -71,7 +63,7 @@ class QueryTest extends \PHPUnit_Framework_TestCase
         $q->add('facet', 'width');
         $q->add('facet.field', 'foo');
         // Use the duplicate aggregator
-        $q->setAggregator(new DuplicateAggregator());
+        $q->setAggregator($q::duplicateAggregator());
         $this->assertEquals('facet=size&facet=width&facet.field=foo', (string) $q);
     }
 
@@ -173,4 +165,61 @@ class QueryTest extends \PHPUnit_Framework_TestCase
     {
         $this->assertEquals('', (string) Query::fromString(''));
     }
+
+    private $encodeData = [
+        't' => [
+            'v1' => ['a', '1'],
+            'v2' => 'b',
+            'v3' => ['v4' => 'c', 'v5' => 'd']
+        ]
+    ];
+
+    public function testEncodesDuplicateAggregator()
+    {
+        $agg = Query::duplicateAggregator();
+        $result = $agg($this->encodeData);
+        $this->assertEquals(array(
+            't[v1]' => ['a', '1'],
+            't[v2]' => ['b'],
+            't[v3][v4]' => ['c'],
+            't[v3][v5]' => ['d'],
+        ), $result);
+    }
+
+    public function testDuplicateEncodesNoNumericIndices()
+    {
+        $agg = Query::duplicateAggregator();
+        $result = $agg($this->encodeData);
+        $this->assertEquals(array(
+            't[v1]' => ['a', '1'],
+            't[v2]' => ['b'],
+            't[v3][v4]' => ['c'],
+            't[v3][v5]' => ['d'],
+        ), $result);
+    }
+
+    public function testEncodesPhpAggregator()
+    {
+        $agg = Query::phpAggregator();
+        $result = $agg($this->encodeData);
+        $this->assertEquals(array(
+            't[v1][0]' => ['a'],
+            't[v1][1]' => ['1'],
+            't[v2]' => ['b'],
+            't[v3][v4]' => ['c'],
+            't[v3][v5]' => ['d'],
+        ), $result);
+    }
+
+    public function testPhpEncodesNoNumericIndices()
+    {
+        $agg = Query::phpAggregator(false);
+        $result = $agg($this->encodeData);
+        $this->assertEquals(array(
+            't[v1][]' => ['a', '1'],
+            't[v2]' => ['b'],
+            't[v3][v4]' => ['c'],
+            't[v3][v5]' => ['d'],
+        ), $result);
+    }
 }