diff --git a/sessionctx/variable/session.go b/sessionctx/variable/session.go
index 9a8e18a05d8c6..d08ab8cd7d51b 100644
--- a/sessionctx/variable/session.go
+++ b/sessionctx/variable/session.go
@@ -1301,6 +1301,7 @@ func NewSessionVars() *SessionVars {
 		EnableLegacyInstanceScope:   DefEnableLegacyInstanceScope,
 		RemoveOrderbyInSubquery:     DefTiDBRemoveOrderbyInSubquery,
 		MaxAllowedPacket:            DefMaxAllowedPacket,
+		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 6c62a697e6d5b..1624977791c42 100644
--- a/sessionctx/variable/sysvar_test.go
+++ b/sessionctx/variable/sysvar_test.go
@@ -986,3 +986,14 @@ func TestTiDBCommitterConcurrency(t *testing.T) {
 	require.Equal(t, val, fmt.Sprintf("%d", expected))
 	require.NoError(t, err)
 }
+
+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)
+}