diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index cf901a64..973b0030 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -13,7 +13,7 @@ jobs:
       matrix:
         module: [ '', 'provider/file', 'provider/pflag', 'provider/appconfig' ]
         run-on: [ 'ubuntu', 'macOS', 'windows' ]
-        go-version: [ 'stable' ]
+        go-version: [ 'stable', 'oldstable' ]
     name: Test
     runs-on: ${{ matrix.run-on }}-latest
     steps:
diff --git a/provider/flag/benchmark_test.go b/provider/flag/benchmark_test.go
index 0690eb6a..4d39a949 100644
--- a/provider/flag/benchmark_test.go
+++ b/provider/flag/benchmark_test.go
@@ -4,7 +4,6 @@
 package flag_test
 
 import (
-	"flag"
 	"testing"
 
 	"github.com/nil-go/konf/internal/assert"
@@ -12,8 +11,6 @@ import (
 )
 
 func BenchmarkNew(b *testing.B) {
-	set := &flag.FlagSet{}
-	set.String("k", "v", "")
 	b.ResetTimer()
 
 	var loader kflag.Flag
@@ -28,8 +25,6 @@ func BenchmarkNew(b *testing.B) {
 }
 
 func BenchmarkLoad(b *testing.B) {
-	set := &flag.FlagSet{}
-	set.String("k", "v", "")
 	loader := kflag.New(konf{}, kflag.WithFlagSet(set))
 	b.ResetTimer()
 
diff --git a/provider/flag/flag_test.go b/provider/flag/flag_test.go
index 527725e1..c8a16a1f 100644
--- a/provider/flag/flag_test.go
+++ b/provider/flag/flag_test.go
@@ -33,7 +33,14 @@ func TestFlag_Load(t *testing.T) {
 	}{
 		{
 			description: "with flag set",
-			opts:        []kflag.Option{kflag.WithFlagSet(set), kflag.WithDelimiter("_")},
+			opts:        []kflag.Option{kflag.WithFlagSet(set)},
+			expected: map[string]any{
+				"k": "v",
+			},
+		},
+		{
+			description: "with delimiter",
+			opts:        []kflag.Option{kflag.WithDelimiter("_"), kflag.WithPrefix("p_")},
 			expected: map[string]any{
 				"p": map[string]any{
 					"d": "_",
@@ -121,6 +128,7 @@ func init() {
 	_ = flag.Set("p.k", "v")
 	flag.String("p.d", ".", "")
 	flag.Int("p.i", 0, "")
+	flag.String("p_d", "_", "")
 
-	set.String("p_d", "_", "")
+	set.String("k", "v", "")
 }
diff --git a/provider/pflag/benchmark_test.go b/provider/pflag/benchmark_test.go
index 7a6e3fbf..1c5f2d00 100644
--- a/provider/pflag/benchmark_test.go
+++ b/provider/pflag/benchmark_test.go
@@ -6,15 +6,11 @@ package pflag_test
 import (
 	"testing"
 
-	"github.com/spf13/pflag"
-
 	kflag "github.com/nil-go/konf/provider/pflag"
 	"github.com/nil-go/konf/provider/pflag/internal/assert"
 )
 
 func BenchmarkNew(b *testing.B) {
-	set := &pflag.FlagSet{}
-	set.String("k", "v", "")
 	b.ResetTimer()
 
 	var loader kflag.PFlag
@@ -29,8 +25,6 @@ func BenchmarkNew(b *testing.B) {
 }
 
 func BenchmarkLoad(b *testing.B) {
-	set := &pflag.FlagSet{}
-	set.String("k", "v", "")
 	loader := kflag.New(konf{}, kflag.WithFlagSet(set))
 	b.ResetTimer()
 
diff --git a/provider/pflag/pflag_test.go b/provider/pflag/pflag_test.go
index 95aef358..d9e35ee9 100644
--- a/provider/pflag/pflag_test.go
+++ b/provider/pflag/pflag_test.go
@@ -36,6 +36,13 @@ func TestPFlag_Load(t *testing.T) {
 		{
 			description: "with flag set",
 			opts:        []kflag.Option{kflag.WithFlagSet(set), kflag.WithDelimiter("_")},
+			expected: map[string]any{
+				"k": "v",
+			},
+		},
+		{
+			description: "with delimiter",
+			opts:        []kflag.Option{kflag.WithDelimiter("_"), kflag.WithPrefix("p_")},
 			expected: map[string]any{
 				"p": map[string]any{
 					"d": "_",
@@ -124,7 +131,8 @@ func init() {
 	_ = pflag.Set("p.k", "v")
 	pflag.String("p.d", ".", "")
 	pflag.Int("p.i", 0, "")
+	pflag.String("p_d", "_", "")
 	pflag.Parse()
 
-	set.String("p_d", "_", "")
+	set.String("k", "v", "")
 }