diff --git a/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala
index 3b76aaf7d0e0daabe1f6b6aa1562fa6974b87193..64b4718538e29683687bbf1e593afa31acf7b738 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/StringFunctionsSuite.scala
@@ -95,7 +95,7 @@ class StringFunctionsSuite extends QueryTest with SharedSQLContext {
   }
 
   test("non-matching optional group") {
-    val df = Seq("aaaac").toDF("s")
+    val df = Seq(Tuple1("aaaac")).toDF("s")
     checkAnswer(
       df.select(regexp_extract($"s", "(a+)(b)?(c)", 2)),
       Row("")