diff --git a/x/sync/workheap_test.go b/x/sync/workheap_test.go
index 0e48f66be26e..7f50468a1fbd 100644
--- a/x/sync/workheap_test.go
+++ b/x/sync/workheap_test.go
@@ -4,13 +4,17 @@
 package sync
 
 import (
+	"math/rand"
 	"testing"
-
-	"github.com/ava-labs/avalanchego/utils/maybe"
+	"time"
 
 	"github.com/stretchr/testify/require"
 
+	"golang.org/x/exp/slices"
+
 	"github.com/ava-labs/avalanchego/ids"
+	"github.com/ava-labs/avalanchego/utils"
+	"github.com/ava-labs/avalanchego/utils/maybe"
 )
 
 // Tests heap.Interface methods Push, Pop, Swap, Len, Less.
@@ -271,3 +275,135 @@ func Test_WorkHeap_Merge_Insert(t *testing.T) {
 	syncHeap.MergeInsert(&workItem{start: maybe.Some([]byte{63}), end: maybe.Some([]byte{127}), priority: lowPriority})
 	require.Equal(t, 1, syncHeap.Len())
 }
+
+func TestWorkHeapMergeInsertRandom(t *testing.T) {
+	var (
+		require   = require.New(t)
+		seed      = time.Now().UnixNano()
+		rand      = rand.New(rand.NewSource(seed)) // #nosec G404
+		numRanges = 1_000
+		bounds    = [][]byte{}
+		rootID    = ids.GenerateTestID()
+	)
+	t.Logf("seed: %d", seed)
+
+	// Create start and end bounds
+	for i := 0; i < numRanges; i++ {
+		bound := make([]byte, 32)
+		_, _ = rand.Read(bound)
+		bounds = append(bounds, bound)
+	}
+	utils.SortBytes(bounds)
+
+	// Note that start < end for all ranges.
+	// It is possible but extremely unlikely that
+	// two elements of [bounds] are equal.
+	ranges := []workItem{}
+	for i := 0; i < numRanges/2; i++ {
+		start := bounds[i*2]
+		end := bounds[i*2+1]
+		ranges = append(ranges, workItem{
+			start:    maybe.Some(start),
+			end:      maybe.Some(end),
+			priority: lowPriority,
+			// Note they all share the same root ID.
+			localRootID: rootID,
+		})
+	}
+	// Set beginning of first range to Nothing.
+	ranges[0].start = maybe.Nothing[[]byte]()
+	// Set end of last range to Nothing.
+	ranges[len(ranges)-1].end = maybe.Nothing[[]byte]()
+
+	setup := func() *workHeap {
+		// Insert all the ranges into the heap.
+		h := newWorkHeap()
+		for i, r := range ranges {
+			require.Equal(i, h.Len())
+			rCopy := r
+			h.MergeInsert(&rCopy)
+		}
+		return h
+	}
+
+	{
+		// Case 1: Merging an item with the range before and after
+		h := setup()
+		// Keep merging ranges until there's only one range left.
+		for i := 0; i < len(ranges)-1; i++ {
+			// Merge ranges[i] with ranges[i+1]
+			h.MergeInsert(&workItem{
+				start:       ranges[i].end,
+				end:         ranges[i+1].start,
+				priority:    lowPriority,
+				localRootID: rootID,
+			})
+			require.Equal(len(ranges)-i-1, h.Len())
+		}
+		got := h.GetWork()
+		require.True(got.start.IsNothing())
+		require.True(got.end.IsNothing())
+	}
+
+	{
+		// Case 2: Merging an item with the range before
+		h := setup()
+		for i := 0; i < len(ranges)-1; i++ {
+			// Extend end of ranges[i]
+			newEnd := slices.Clone(ranges[i].end.Value())
+			newEnd = append(newEnd, 0)
+			h.MergeInsert(&workItem{
+				start:       ranges[i].end,
+				end:         maybe.Some(newEnd),
+				priority:    lowPriority,
+				localRootID: rootID,
+			})
+
+			// Shouldn't cause number of elements to change
+			require.Equal(len(ranges), h.Len())
+
+			start := ranges[i].start
+			if i == 0 {
+				start = maybe.Nothing[[]byte]()
+			}
+			// Make sure end is updated
+			got, ok := h.sortedItems.Get(&heapItem{
+				workItem: &workItem{
+					start: start,
+				},
+			})
+			require.True(ok)
+			require.Equal(newEnd, got.workItem.end.Value())
+		}
+	}
+
+	{
+		// Case 3: Merging an item with the range after
+		h := setup()
+		for i := 1; i < len(ranges); i++ {
+			// Extend start of ranges[i]
+			newStartBytes := slices.Clone(ranges[i].start.Value())
+			newStartBytes = newStartBytes[:len(newStartBytes)-1]
+			newStart := maybe.Some(newStartBytes)
+
+			h.MergeInsert(&workItem{
+				start:       newStart,
+				end:         ranges[i].start,
+				priority:    lowPriority,
+				localRootID: rootID,
+			})
+
+			// Shouldn't cause number of elements to change
+			require.Equal(len(ranges), h.Len())
+
+			// Make sure start is updated
+			got, ok := h.sortedItems.Get(&heapItem{
+				workItem: &workItem{
+					start: newStart,
+				},
+			})
+			require.True(ok)
+			require.Equal(newStartBytes, got.workItem.start.Value())
+		}
+	}
+}