diff --git a/sjson.go b/sjson.go
index 797469b..7f1d358 100644
--- a/sjson.go
+++ b/sjson.go
@@ -128,7 +128,7 @@ func appendBuild(buf []byte, array bool, paths []pathResult, raw string,
 	}
 	if len(paths) > 1 {
 		n, numeric := atoui(paths[1])
-		if numeric {
+		if numeric || (!paths[1].force && paths[1].part == "-1") {
 			buf = append(buf, '[')
 			buf = appendRepeat(buf, "null,", n)
 			buf = appendBuild(buf, true, paths[1:], raw, stringify)
diff --git a/sjson_test.go b/sjson_test.go
index b0983cd..a7a8f7e 100644
--- a/sjson_test.go
+++ b/sjson_test.go
@@ -141,6 +141,7 @@ func TestBasic(t *testing.T) {
 	testRaw(t, setString, `["1234.5"]`, ``, `0`, "1234.5")
 	testRaw(t, setBool, `[true]`, ``, `0`, true)
 	testRaw(t, setBool, `[null]`, ``, `0`, nil)
+	testRaw(t, setString, `{"arr":[1]}`, ``, `arr.-1`, 1)
 }
 
 func TestDelete(t *testing.T) {