diff --git a/level_121.go b/level_121.go
deleted file mode 100644
index c602bef..0000000
--- a/level_121.go
+++ /dev/null
@@ -1,15 +0,0 @@
-//go:build go1.21
-// +build go1.21
-
-package log
-
-import "log/slog"
-
-// fromSlogLevel converts slog.Level to log.Level.
-var fromSlogLevel = map[slog.Level]Level{
-	slog.LevelDebug: DebugLevel,
-	slog.LevelInfo:  InfoLevel,
-	slog.LevelWarn:  WarnLevel,
-	slog.LevelError: ErrorLevel,
-	slog.Level(12):  FatalLevel,
-}
diff --git a/level_no121.go b/level_no121.go
deleted file mode 100644
index b505c08..0000000
--- a/level_no121.go
+++ /dev/null
@@ -1,15 +0,0 @@
-//go:build !go1.21
-// +build !go1.21
-
-package log
-
-import "golang.org/x/exp/slog"
-
-// fromSlogLevel converts slog.Level to log.Level.
-var fromSlogLevel = map[slog.Level]Level{
-	slog.LevelDebug: DebugLevel,
-	slog.LevelInfo:  InfoLevel,
-	slog.LevelWarn:  WarnLevel,
-	slog.LevelError: ErrorLevel,
-	slog.Level(12):  FatalLevel,
-}
diff --git a/logger_121.go b/logger_121.go
index 885b6cf..cd49a09 100644
--- a/logger_121.go
+++ b/logger_121.go
@@ -14,7 +14,7 @@ import (
 //
 // Implements slog.Handler.
 func (l *Logger) Enabled(_ context.Context, level slog.Level) bool {
-	return atomic.LoadInt32(&l.level) <= int32(fromSlogLevel[level])
+	return atomic.LoadInt32(&l.level) <= int32(level)
 }
 
 // Handle handles the Record. It will only be called if Enabled returns true.
@@ -33,7 +33,7 @@ func (l *Logger) Handle(ctx context.Context, record slog.Record) error {
 	// Get the caller frame using the record's PC.
 	frames := runtime.CallersFrames([]uintptr{record.PC})
 	frame, _ := frames.Next()
-	l.handle(fromSlogLevel[record.Level], l.timeFunc(record.Time), []runtime.Frame{frame}, record.Message, fields...)
+	l.handle(Level(record.Level), l.timeFunc(record.Time), []runtime.Frame{frame}, record.Message, fields...)
 	return nil
 }
 
diff --git a/logger_121_test.go b/logger_121_test.go
index e57f318..d893ebc 100644
--- a/logger_121_test.go
+++ b/logger_121_test.go
@@ -5,7 +5,9 @@ package log
 
 import (
 	"bytes"
+	"context"
 	"testing"
+	"time"
 
 	"log/slog"
 
@@ -149,3 +151,35 @@ func TestSlogWithGroup(t *testing.T) {
 		})
 	}
 }
+
+func TestSlogCustomLevel(t *testing.T) {
+	var buf bytes.Buffer
+	cases := []struct {
+		name     string
+		expected string
+		level    slog.Level
+		minLevel Level
+	}{
+		{
+			name:     "custom level not enabled",
+			expected: "",
+			level:    slog.Level(500),
+			minLevel: Level(600),
+		},
+		{
+			name:     "custom level enabled",
+			expected: "foo\n",
+			level:    slog.Level(500),
+			minLevel: Level(100),
+		},
+	}
+	for _, c := range cases {
+		buf.Reset()
+		t.Run(c.name, func(t *testing.T) {
+			l := New(&buf)
+			l.SetLevel(c.minLevel)
+			l.Handle(context.Background(), slog.NewRecord(time.Now(), c.level, "foo", 0))
+			assert.Equal(t, c.expected, buf.String())
+		})
+	}
+}
diff --git a/logger_no121.go b/logger_no121.go
index aa602d1..bf2eaf9 100644
--- a/logger_no121.go
+++ b/logger_no121.go
@@ -15,7 +15,7 @@ import (
 //
 // Implements slog.Handler.
 func (l *Logger) Enabled(_ context.Context, level slog.Level) bool {
-	return atomic.LoadInt32(&l.level) <= int32(fromSlogLevel[level])
+	return atomic.LoadInt32(&l.level) <= int32(level)
 }
 
 // Handle handles the Record. It will only be called if Enabled returns true.
@@ -30,7 +30,7 @@ func (l *Logger) Handle(_ context.Context, record slog.Record) error {
 	// Get the caller frame using the record's PC.
 	frames := runtime.CallersFrames([]uintptr{record.PC})
 	frame, _ := frames.Next()
-	l.handle(fromSlogLevel[record.Level], l.timeFunc(record.Time), []runtime.Frame{frame}, record.Message, fields...)
+	l.handle(Level(record.Level), l.timeFunc(record.Time), []runtime.Frame{frame}, record.Message, fields...)
 	return nil
 }