diff --git a/internal/buffer/buffer.go b/internal/buffer/buffer.go
index 834c027108..03c45d0de9 100644
--- a/internal/buffer/buffer.go
+++ b/internal/buffer/buffer.go
@@ -1291,7 +1291,12 @@ func (b *Buffer) updateDiffSync() {
 	}
 
 	differ := dmp.New()
-	baseRunes, bufferRunes, _ := differ.DiffLinesToRunes(string(b.diffBase), string(b.Bytes()))
+
+	b.Lock()
+	bytes := b.Bytes()
+	b.Unlock()
+
+	baseRunes, bufferRunes, _ := differ.DiffLinesToRunes(string(b.diffBase), string(bytes))
 	diffs := differ.DiffMainRunes(baseRunes, bufferRunes, false)
 	lineN := 0