diff --git a/src/Olivebbs/Map/GenericMap.php b/src/Olivebbs/Map/GenericMap.php
index ae06c04..a438344 100644
--- a/src/Olivebbs/Map/GenericMap.php
+++ b/src/Olivebbs/Map/GenericMap.php
@@ -31,13 +31,13 @@ use ArrayAccess;
 use Countable;
 use Ds\Map;
 use function is_array;
+use function is_callable;
 use function is_int;
 use function is_object;
 use function is_string;
-use function mb_strlen;
-use function strtolower;
-
 use Olivebbs\Map\Exception\InvalidArgumentException;
+
+use function strtolower;
 use TypeError;
 use ValueError;
 
@@ -56,18 +56,11 @@ class GenericMap implements ArrayAccess, Countable
     protected string $keyType;
     protected string $valueType;
 
-    public function __construct(?string $keyType = null, ?string $valueType = null)
+    public function __construct(string $keyType = self::ANY, string $valueType = self::ANY)
     {
+        $this->keyType = strtolower($keyType);
 
-
-
-        $this->keyType = strtolower($keyType ?? self::ANY);
-
-        $this->valueType = $valueType ?? self::ANY;
-
-        if(!class_exists($this->valueType)) {
-            $this->valueType = strtolower($this->valueType);
-        }
+        $this->valueType = class_exists($valueType) ? $valueType : strtolower($valueType);
 
         if (!$this->isValidKeyType($this->keyType)) {
             throw new InvalidArgumentException(sprintf('Invalid key type (%s)', $this->keyType));
@@ -96,7 +89,7 @@ class GenericMap implements ArrayAccess, Countable
     public function offsetExists($offset): bool
     {
         if (is_array($offset) || is_object($offset)) {
-            throw new InvalidArgumentException('Map Keys cannot be objects or arrays');
+            throw new InvalidArgumentException('Map keys cannot be objects or arrays');
         }
 
         if (!$this->checkType($this->keyType, $offset)) {
@@ -112,7 +105,7 @@ class GenericMap implements ArrayAccess, Countable
     public function offsetGet($offset)
     {
         if (is_array($offset) || is_object($offset)) {
-            throw new InvalidArgumentException('Map Keys cannot be objects or arrays');
+            throw new InvalidArgumentException('Map keys cannot be objects or arrays');
         }
 
         if (!$this->checkType($this->keyType, $offset)) {
@@ -130,7 +123,7 @@ class GenericMap implements ArrayAccess, Countable
     public function offsetSet($offset, $value): void
     {
         if (is_array($offset) || is_object($offset)) {
-            throw new InvalidArgumentException('Map Keys cannot be objects or arrays');
+            throw new InvalidArgumentException('Map keys cannot be objects or arrays');
         }
 
         if (!$this->checkType($this->keyType, $offset)) {
@@ -150,7 +143,7 @@ class GenericMap implements ArrayAccess, Countable
     public function offsetUnset($offset): void
     {
         if (is_array($offset) || is_object($offset)) {
-            throw new InvalidArgumentException('Map Keys cannot be objects or arrays');
+            throw new InvalidArgumentException('Map keys cannot be objects or arrays');
         }
 
         if (!$this->checkType($this->keyType, $offset)) {
@@ -202,6 +195,8 @@ class GenericMap implements ArrayAccess, Countable
         switch ($type) {
             case self::OBJECT:
                 return is_object($var);
+            case self::CALLABLE:
+                return is_callable($var);
             case self::ARRAY:
                 return is_array($var);
             case self::INT:
@@ -210,7 +205,7 @@ class GenericMap implements ArrayAccess, Countable
             case self::STRING:
                 return is_string($var);
             case self::CHAR:
-                return is_string($var) && mb_strlen($var) === 1;
+                return is_string($var) && \mb_strlen($var) === 1;
             case self::ANY:
                 return true;
             default:
@@ -230,7 +225,7 @@ class GenericMap implements ArrayAccess, Countable
 
     private function isValidValueType(string $type): bool
     {
-        if(class_exists($type)) {
+        if (class_exists($type)) {
             return true;
         }
 
diff --git a/tests/GenericMapTest.php b/tests/GenericMapTest.php
index 1e045fb..77379e6 100644
--- a/tests/GenericMapTest.php
+++ b/tests/GenericMapTest.php
@@ -156,7 +156,15 @@ class GenericMapTest extends TestCase
         $genericMap[0] = $splObject;
         self::assertSame($splObject, $genericMap[0]);
         self::assertTrue($genericMap[0]->contains($stdClass));
+    }
 
+    public function testObjectCantBeUsedAsKeyWithAny(): void
+    {
+        $genericMap = new GenericMap(GenericMap::ANY, GenericMap::ANY);
+        $object = new \SplObjectStorage();
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Map keys cannot be objects or arrays');
+        $genericMap[$object] = 1;
     }
 
     private function resetGenericMap(): void