diff --git a/sessionctx/variable/session.go b/sessionctx/variable/session.go
index d392c1de8f5a2..71fd2af162997 100644
--- a/sessionctx/variable/session.go
+++ b/sessionctx/variable/session.go
@@ -1960,6 +1960,7 @@ func NewSessionVars(hctx HookContext) *SessionVars {
 		mppVersion:                    kv.MppVersionUnspecified,
 		EnableLateMaterialization:     DefTiDBOptEnableLateMaterialization,
 		TiFlashComputeDispatchPolicy:  tiflashcompute.DispatchPolicyConsistentHash,
+		EnableWindowFunction:          DefEnableWindowFunction,
 	}
 	vars.KVVars = tikvstore.NewVariables(&vars.Killed)
 	vars.Concurrency = Concurrency{
diff --git a/sessionctx/variable/sysvar_test.go b/sessionctx/variable/sysvar_test.go
index 568d7a45691dd..a37ad725a8555 100644
--- a/sessionctx/variable/sysvar_test.go
+++ b/sessionctx/variable/sysvar_test.go
@@ -1238,3 +1238,14 @@ func TestTiDBEnableRowLevelChecksum(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, Off, val)
 }
+
+func TestEnableWindowFunction(t *testing.T) {
+	vars := NewSessionVars(nil)
+	require.Equal(t, vars.EnableWindowFunction, DefEnableWindowFunction)
+	require.NoError(t, vars.SetSystemVar(TiDBEnableWindowFunction, "on"))
+	require.Equal(t, vars.EnableWindowFunction, true)
+	require.NoError(t, vars.SetSystemVar(TiDBEnableWindowFunction, "0"))
+	require.Equal(t, vars.EnableWindowFunction, false)
+	require.NoError(t, vars.SetSystemVar(TiDBEnableWindowFunction, "1"))
+	require.Equal(t, vars.EnableWindowFunction, true)
+}