diff --git a/2023/04.cpp b/2023/04.cpp
index 0855b5e..6c6bf35 100644
--- a/2023/04.cpp
+++ b/2023/04.cpp
@@ -72,11 +72,10 @@ auto Part1(std::vector<std::size_t> const& wins) -> std::uint64_t
 
 auto Part2(std::vector<std::size_t> const& wins) -> std::size_t
 {
-  std::vector<std::size_t> psums(wins);
-  psums.push_back(0);
+  std::vector<std::size_t> psums(wins.size() + 1);
   for (std::size_t i = wins.size(); i --> 0;)
   {
-    psums[i] = 1 + 2 * psums[i+1] - psums[1 + i + psums[i]];
+    psums[i] = 1 + 2 * psums[i + 1] - psums[i + 1 + wins[i]];
   }
   return psums.front();
 }