diff --git a/pkl-core/src/main/java/org/pkl/core/stdlib/base/MergeSort.java b/pkl-core/src/main/java/org/pkl/core/stdlib/base/MergeSort.java
index b07a2388..e3885c2b 100644
--- a/pkl-core/src/main/java/org/pkl/core/stdlib/base/MergeSort.java
+++ b/pkl-core/src/main/java/org/pkl/core/stdlib/base/MergeSort.java
@@ -58,7 +58,7 @@ final class MergeSort {
       SortComparatorNode comparator,
       @Nullable VmFunction function) {
 
-    if (comparator.executeWith(array[mid], array[mid], function)) {
+    if (comparator.executeWith(array[mid-1], array[mid], function)) {
       return; // already sorted
     }