diff --git a/Heap/Heap.swift b/Heap/Heap.swift
index 7560bc7b9..42f20ca03 100755
--- a/Heap/Heap.swift
+++ b/Heap/Heap.swift
@@ -209,7 +209,7 @@ extension Heap where T: Equatable {
   
   /** Get the index of a node in the heap. Performance: O(n). */
   public func index(of node: T) -> Int? {
-    return nodes.index(where: { $0 == node })
+    return nodes.firstIndex(where: { $0 == node })
   }
   
   /** Removes the first occurrence of a node from the heap. Performance: O(n). */