diff --git a/src/Validator/Rules/KnownDirectives.php b/src/Validator/Rules/KnownDirectives.php
index e9a0b8c..519f50c 100644
--- a/src/Validator/Rules/KnownDirectives.php
+++ b/src/Validator/Rules/KnownDirectives.php
@@ -11,6 +11,7 @@ use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\NodeList;
 use GraphQL\Language\DirectiveLocation;
+use GraphQL\Type\Definition\Directive;
 use GraphQL\Validator\ValidationContext;
 use function count;
 use function in_array;
@@ -18,40 +19,51 @@ use function sprintf;
 
 class KnownDirectives extends ValidationRule
 {
+    /**
+     * @param ValidationContext $context
+     * @return array
+     */
     public function getVisitor(ValidationContext $context)
     {
-        return [
-            NodeKind::DIRECTIVE => function (DirectiveNode $node, $key, $parent, $path, $ancestors) use ($context) {
-                $directiveDef = null;
-                foreach ($context->getSchema()->getDirectives() as $def) {
-                    if ($def->name === $node->name->value) {
-                        $directiveDef = $def;
-                        break;
-                    }
-                }
+        $locationsMap = [];
+        $schema = $context->getSchema();
 
-                if (! $directiveDef) {
+        $definedDirectives = $schema ? $schema->getDirectives() : Directive::getInternalDirectives();
+
+        foreach ($definedDirectives as $directive) {
+            $locationsMap[$directive->name] = $directive->locations;
+        }
+
+        $astDefinition = $context->getDocument()->definitions;
+        foreach ($astDefinition as $def) {
+            if ($def->kind === NodeKind::DIRECTIVE_DEFINITION) {
+                $locationsMap[$def->name->value] = array_map(function ($name) {
+                    return $name->value;
+                }, $def->locations);
+            }
+        }
+        return [
+            NodeKind::DIRECTIVE => function (DirectiveNode $node, $key, $parent, $path, $ancestors) use ($context, $locationsMap) {
+                $name = $node->name->value;
+                $locations = $locationsMap[$name] ?? null;
+
+                if (!$locations) {
                     $context->reportError(new Error(
-                        self::unknownDirectiveMessage($node->name->value),
+                        self::unknownDirectiveMessage($name),
                         [$node]
                     ));
-
                     return;
                 }
+
                 $candidateLocation = $this->getDirectiveLocationForASTPath($ancestors);
 
-                if (! $candidateLocation) {
+                if ($candidateLocation && !in_array($candidateLocation, $locations)) {
                     $context->reportError(new Error(
-                        self::misplacedDirectiveMessage($node->name->value, $node->type),
-                        [$node]
-                    ));
-                } elseif (! in_array($candidateLocation, $directiveDef->locations)) {
-                    $context->reportError(new Error(
-                        self::misplacedDirectiveMessage($node->name->value, $candidateLocation),
+                        self::misplacedDirectiveMessage($name, $candidateLocation),
                         [$node]
                     ));
                 }
-            },
+            }
         ];
     }
 
@@ -88,6 +100,7 @@ class KnownDirectives extends ValidationRule
             case NodeKind::FRAGMENT_DEFINITION:
                 return DirectiveLocation::FRAGMENT_DEFINITION;
             case NodeKind::SCHEMA_DEFINITION:
+            case NodeKind::SCHEMA_EXTENSION:
                 return DirectiveLocation::SCHEMA;
             case NodeKind::SCALAR_TYPE_DEFINITION:
             case NodeKind::SCALAR_TYPE_EXTENSION: