diff --git a/src/Sorter/TopologicalSorter.php b/src/Sorter/TopologicalSorter.php
index 83cd111f..29b4313f 100644
--- a/src/Sorter/TopologicalSorter.php
+++ b/src/Sorter/TopologicalSorter.php
@@ -186,7 +186,7 @@ private function visit(Vertex $definition)
         $this->sortedNodeList[] = $definition->value;
     }
 
-    public function getDefinition(string $dependency, Vertex $definition): Vertex
+    private function getDefinition(string $dependency, Vertex $definition): Vertex
     {
         if (! isset($this->nodeList[$dependency])) {
             throw new RuntimeException(sprintf(