diff --git a/src/Utils/SchemaPrinter.php b/src/Utils/SchemaPrinter.php
index 1c56648..3eed8fa 100644
--- a/src/Utils/SchemaPrinter.php
+++ b/src/Utils/SchemaPrinter.php
@@ -159,7 +159,7 @@ class SchemaPrinter
     {
         $interfaces = $type->getInterfaces();
         $implementedInterfaces = !empty($interfaces) ?
-            ' implements ' . implode(', ', array_map(function($i) {
+            ' implements ' . implode(' & ', array_map(function($i) {
                 return $i->name;
             }, $interfaces)) : '';
         return self::printDescription($options, $type) .
diff --git a/tests/Utils/SchemaPrinterTest.php b/tests/Utils/SchemaPrinterTest.php
index db09452..a6f543a 100644
--- a/tests/Utils/SchemaPrinterTest.php
+++ b/tests/Utils/SchemaPrinterTest.php
@@ -21,7 +21,9 @@ class SchemaPrinterTest extends TestCase
 
     private function printForTest($schema)
     {
-        return "\n" . SchemaPrinter::doPrint($schema);
+        $schemaText = SchemaPrinter::doPrint($schema);
+        $this->assertEquals($schemaText, SchemaPrinter::doPrint(BuildSchema::build($schemaText)));
+        return "\n" . $schemaText;
     }
 
     private function printSingleFieldSchema($fieldConfig)
@@ -464,7 +466,7 @@ interface Baaz {
   int: Int
 }
 
-type Bar implements Foo, Baaz {
+type Bar implements Foo & Baaz {
   str: String
   int: Int
 }