diff --git a/src/STLVertex.php b/src/STLVertex.php
index 966d1a9..27fc0ab 100644
--- a/src/STLVertex.php
+++ b/src/STLVertex.php
@@ -120,7 +120,7 @@ public function toArray() : array
     public function toString() : string
     {
         $coordinates = $this->getCoordinatesArray();
-        $string = "outerloop\n";
+        $string = "outer loop\n";
         foreach ($coordinates as $coordinate) {
             $string .= "    vertex " . implode(" ", $coordinate) . "\n";
         }
@@ -128,4 +128,4 @@ public function toString() : string
 
         return $string;
     }
-}
\ No newline at end of file
+}