diff --git a/backends-clickhouse/src/test/scala/org/apache/gluten/execution/GlutenFunctionValidateSuite.scala b/backends-clickhouse/src/test/scala/org/apache/gluten/execution/GlutenFunctionValidateSuite.scala
index 6a0196e2b18..66ea6c98669 100644
--- a/backends-clickhouse/src/test/scala/org/apache/gluten/execution/GlutenFunctionValidateSuite.scala
+++ b/backends-clickhouse/src/test/scala/org/apache/gluten/execution/GlutenFunctionValidateSuite.scala
@@ -489,6 +489,20 @@ class GlutenFunctionValidateSuite extends GlutenClickHouseWholeStageTransformerS
     runQueryAndCompare(sql1)(checkGlutenPlan[ProjectExecTransformer])
   }
 
+  test("test str2map with nullable string input") {
+    val sql =
+      """
+        |select id, str_to_map(str, ',', ':')
+        |from (
+        |  select id,
+        |    if(id = 1, cast(null as string), concat('k:', cast(id as string))) as str
+        |  from range(4)
+        |)
+        |order by id
+        |""".stripMargin
+    runQueryAndCompare(sql)(checkGlutenPlan[ProjectExecTransformer])
+  }
+
   test("test parse_url") {
     val sql1 =
       """
diff --git a/cpp-ch/local-engine/Functions/SparkFunctionStrToMap.cpp b/cpp-ch/local-engine/Functions/SparkFunctionStrToMap.cpp
index 8936ea0d04b..e9c1d80c066 100644
--- a/cpp-ch/local-engine/Functions/SparkFunctionStrToMap.cpp
+++ b/cpp-ch/local-engine/Functions/SparkFunctionStrToMap.cpp
@@ -240,7 +240,7 @@ class SparkFunctionStrToMap : public DB::IFunction
 
         for (size_t i = 0, n = offsets.size(); i < n; ++i)
         {
-            if (null_map && (*null_map)[n] != 0)
+            if (null_map && (*null_map)[i] != 0)
                 col_map->insertDefault();
             else
             {