diff --git a/src/Utils/MixedStore.php b/src/Utils/MixedStore.php
index 9811ba7..76d5444 100644
--- a/src/Utils/MixedStore.php
+++ b/src/Utils/MixedStore.php
@@ -16,7 +16,12 @@ class MixedStore implements \ArrayAccess
     /**
      * @var array
      */
-    private $scalarStore;
+    private $standardStore;
+
+    /**
+     * @var array
+     */
+    private $floatStore;
 
     /**
      * @var \SplObjectStorage
@@ -43,15 +48,49 @@ class MixedStore implements \ArrayAccess
      */
     private $lastArrayValue;
 
+    /**
+     * @var mixed
+     */
+    private $nullValue;
+
+    /**
+     * @var bool
+     */
+    private $nullValueIsSet;
+
+    /**
+     * @var mixed
+     */
+    private $trueValue;
+
+    /**
+     * @var bool
+     */
+    private $trueValueIsSet;
+
+    /**
+     * @var mixed
+     */
+    private $falseValue;
+
+    /**
+     * @var bool
+     */
+    private $falseValueIsSet;
+
     /**
      * MixedStore constructor.
      */
     public function __construct()
     {
-        $this->scalarStore = [];
+        $this->standardStore = [];
+        $this->floatStore = [];
         $this->objectStore = new \SplObjectStorage();
         $this->arrayKeys = [];
         $this->arrayValues = [];
+        $this->nullValueIsSet = false;
+        $this->trueValueIsSet = false;
+        $this->falseValueIsSet = false;
     }
 
     /**
@@ -68,8 +107,17 @@ class MixedStore implements \ArrayAccess
      */
     public function offsetExists($offset)
     {
-        if (is_scalar($offset)) {
-            return array_key_exists($offset, $this->scalarStore);
+        if (false === $offset) {
+            return $this->falseValueIsSet;
+        }
+        if (true === $offset) {
+            return $this->trueValueIsSet;
+        }
+        if (is_int($offset) || is_string($offset)) {
+            return array_key_exists($offset, $this->standardStore);
+        }
+        if (is_float($offset)) {
+            return array_key_exists((string) $offset, $this->floatStore);
         }
         if (is_object($offset)) {
             return $this->objectStore->offsetExists($offset);
@@ -83,6 +131,9 @@ class MixedStore implements \ArrayAccess
                 }
             }
         }
+        if (null === $offset) {
+            return $this->nullValueIsSet;
+        }
         return false;
     }
 
@@ -97,8 +148,17 @@ class MixedStore implements \ArrayAccess
      */
     public function offsetGet($offset)
     {
-        if (is_scalar($offset)) {
-            return $this->scalarStore[$offset];
+        if (true === $offset) {
+            return $this->trueValue;
+        }
+        if (false === $offset) {
+            return $this->falseValue;
+        }
+        if (is_int($offset) || is_string($offset)) {
+            return $this->standardStore[$offset];
+        }
+        if (is_float($offset)) {
+            return $this->floatStore[(string)$offset];
         }
         if (is_object($offset)) {
             return $this->objectStore->offsetGet($offset);
@@ -114,6 +174,9 @@ class MixedStore implements \ArrayAccess
                 }
             }
         }
+        if (null === $offset) {
+            return $this->nullValue;
+        }
         return null;
     }
 
@@ -131,13 +194,24 @@ class MixedStore implements \ArrayAccess
      */
     public function offsetSet($offset, $value)
     {
-        if (is_scalar($offset)) {
-            $this->scalarStore[$offset] = $value;
+        if (false === $offset) {
+            $this->falseValue = $value;
+            $this->falseValueIsSet = true;
+        } else if (true === $offset) {
+            $this->trueValue = $value;
+            $this->trueValueIsSet = true;
+        } else if (is_int($offset) || is_string($offset)) {
+            $this->standardStore[$offset] = $value;
+        } else if (is_float($offset)) {
+            $this->floatStore[(string)$offset] = $value;
         } else if (is_object($offset)) {
             $this->objectStore[$offset] = $value;
         } else if (is_array($offset)) {
             $this->arrayKeys[] = $offset;
             $this->arrayValues[] = $value;
+        } else if (null === $offset) {
+            $this->nullValue = $value;
+            $this->nullValueIsSet = true;
         } else {
             throw new \InvalidArgumentException("Unexpected offset type: " . Utils::printSafe($offset));
         }
@@ -154,8 +228,16 @@ class MixedStore implements \ArrayAccess
      */
     public function offsetUnset($offset)
     {
-        if (is_scalar($offset)) {
-            unset($this->scalarStore[$offset]);
+        if (true === $offset) {
+            $this->trueValue = null;
+            $this->trueValueIsSet = false;
+        } else if (false === $offset) {
+            $this->falseValue = null;
+            $this->falseValueIsSet = false;
+        } else if (is_int($offset) || is_string($offset)) {
+            unset($this->standardStore[$offset]);
+        } else if (is_float($offset)) {
+            unset($this->floatStore[(string)$offset]);
         } else if (is_object($offset)) {
             $this->objectStore->offsetUnset($offset);
         } else if (is_array($offset)) {
@@ -165,6 +247,9 @@ class MixedStore implements \ArrayAccess
                 array_splice($this->arrayKeys, $index, 1);
                 array_splice($this->arrayValues, $index, 1);
             }
+        } else if (null === $offset) {
+            $this->nullValue = null;
+            $this->nullValueIsSet = false;
         }
     }
 }
diff --git a/tests/Utils/MixedStoreTest.php b/tests/Utils/MixedStoreTest.php
new file mode 100644
index 0000000..9ebfe6f
--- /dev/null
+++ b/tests/Utils/MixedStoreTest.php
@@ -0,0 +1,126 @@
+<?php
+namespace GraphQL\Tests\Utils;
+
+
+use GraphQL\Utils;
+use GraphQL\Utils\MixedStore;
+
+class MixedStoreTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @var MixedStore
+     */
+    private $mixedStore;
+
+    public function setUp()
+    {
+        $this->mixedStore = new MixedStore();
+    }
+
+    public function getPossibleValues()
+    {
+        return [
+            null,
+            false,
+            true,
+            '',
+            '0',
+            '1',
+            'a',
+            [],
+            new \stdClass(),
+            function() {},
+            new MixedStore()
+        ];
+    }
+
+    public function testAcceptsNullKeys()
+    {
+        foreach ($this->getPossibleValues() as $value) {
+            $this->assertAcceptsKeyValue(null, $value);
+        }
+    }
+
+    public function testAcceptsBoolKeys()
+    {
+        foreach ($this->getPossibleValues() as $value) {
+            $this->assertAcceptsKeyValue(false, $value);
+        }
+        foreach ($this->getPossibleValues() as $value) {
+            $this->assertAcceptsKeyValue(true, $value);
+        }
+    }
+
+    public function testAcceptsIntKeys()
+    {
+        foreach ($this->getPossibleValues() as $value) {
+            $this->assertAcceptsKeyValue(-100000, $value);
+            $this->assertAcceptsKeyValue(-1, $value);
+            $this->assertAcceptsKeyValue(0, $value);
+            $this->assertAcceptsKeyValue(1, $value);
+            $this->assertAcceptsKeyValue(1000000, $value);
+        }
+    }
+
+    public function testAcceptsFloatKeys()
+    {
+        foreach ($this->getPossibleValues() as $value) {
+            $this->assertAcceptsKeyValue(-100000.5, $value);
+            $this->assertAcceptsKeyValue(-1.6, $value);
+            $this->assertAcceptsKeyValue(-0.0001, $value);
+            $this->assertAcceptsKeyValue(0.0000, $value);
+            $this->assertAcceptsKeyValue(0.0001, $value);
+            $this->assertAcceptsKeyValue(1.6, $value);
+            $this->assertAcceptsKeyValue(1000000.5, $value);
+        }
+    }
+
+    public function testAcceptsArrayKeys()
+    {
+        foreach ($this->getPossibleValues() as $value) {
+            $this->assertAcceptsKeyValue([], $value);
+            $this->assertAcceptsKeyValue([null], $value);
+            $this->assertAcceptsKeyValue([[]], $value);
+            $this->assertAcceptsKeyValue([new \stdClass()], $value);
+            $this->assertAcceptsKeyValue(['a', 'b'], $value);
+            $this->assertAcceptsKeyValue(['a' => 'b'], $value);
+        }
+    }
+
+    public function testAcceptsObjectKeys()
+    {
+        foreach ($this->getPossibleValues() as $value) {
+            $this->assertAcceptsKeyValue(new \stdClass(), $value);
+            $this->assertAcceptsKeyValue(new MixedStore(), $value);
+            $this->assertAcceptsKeyValue(function() {}, $value);
+        }
+    }
+
+    private function assertAcceptsKeyValue($key, $value)
+    {
+        $err = 'Failed assertion that MixedStore accepts key ' .
+            Utils::printSafe($key) . ' with value ' .  Utils::printSafe($value);
+
+        $this->assertFalse($this->mixedStore->offsetExists($key), $err);
+        $this->mixedStore->offsetSet($key, $value);
+        $this->assertTrue($this->mixedStore->offsetExists($key), $err);
+        $this->assertSame($value, $this->mixedStore->offsetGet($key), $err);
+        $this->mixedStore->offsetUnset($key);
+        $this->assertFalse($this->mixedStore->offsetExists($key), $err);
+        $this->assertProvidesArrayAccess($key, $value);
+    }
+
+    private function assertProvidesArrayAccess($key, $value)
+    {
+        $err = 'Failed assertion that MixedStore provides array access for key ' .
+            Utils::printSafe($key) . ' with value ' .  Utils::printSafe($value);
+
+        $this->assertFalse(isset($this->mixedStore[$key]), $err);
+        $this->mixedStore[$key] = $value;
+        $this->assertTrue(isset($this->mixedStore[$key]), $err);
+        $this->assertEquals(!empty($value), !empty($this->mixedStore[$key]), $err);
+        $this->assertSame($value, $this->mixedStore[$key], $err);
+        unset($this->mixedStore[$key]);
+        $this->assertFalse(isset($this->mixedStore[$key]), $err);
+    }
+}