diff --git a/CHANGELOG.md b/CHANGELOG.md
index e516cc36..76b8bc18 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,13 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+## [1.2.0] - 2024-06-10
+
+### Changed
+
+- [Breaking] The map key is case insensitive now. If you would like to keep it case sensitive.
+  please add konf.WithMapKeyCaseSensitive option (#365).
+
 ## [1.1.1] - 2024-05-02
 
 ### Fixed
diff --git a/config.go b/config.go
index 2cc0ec6a..01d059a0 100644
--- a/config.go
+++ b/config.go
@@ -28,11 +28,12 @@ type Config struct {
 	nocopy internal.NoCopy[Config]
 
 	// Options.
-	caseSensitive bool
-	delimiter     string
-	logger        *slog.Logger
-	onStatus      func(loader Loader, changed bool, err error)
-	converter     convert.Converter
+	caseSensitive       bool
+	mapKeyCaseSensitive bool
+	delimiter           string
+	logger              *slog.Logger
+	onStatus            func(loader Loader, changed bool, err error)
+	converter           convert.Converter
 
 	// Loaded configuration.
 	values    map[string]any
@@ -162,7 +163,7 @@ func (c *Config) delim() string {
 
 func (c *Config) transformKeys(m map[string]any) {
 	if !c.caseSensitive {
-		maps.TransformKeys(m, strings.ToLower)
+		maps.TransformKeys(m, strings.ToLower, c.mapKeyCaseSensitive)
 	}
 }
 
diff --git a/config_test.go b/config_test.go
index 39592209..c7f8b896 100644
--- a/config_test.go
+++ b/config_test.go
@@ -86,6 +86,16 @@ func TestConfig_Unmarshal(t *testing.T) {
 		{
 			description: "config for map",
 			loaders:     []konf.Loader{mapLoader{"Config": "struct"}},
+			assert: func(config *konf.Config) {
+				var value map[string]string
+				assert.NoError(t, config.Unmarshal("", &value))
+				assert.Equal(t, "struct", value["config"])
+			},
+		},
+		{
+			description: "config for map (case sensitive)",
+			loaders:     []konf.Loader{mapLoader{"Config": "struct"}},
+			opts:        []konf.Option{konf.WithMapKeyCaseSensitive()},
 			assert: func(config *konf.Config) {
 				var value map[string]string
 				assert.NoError(t, config.Unmarshal("", &value))
diff --git a/internal/maps/transform.go b/internal/maps/transform.go
index 711cc652..ed83375f 100644
--- a/internal/maps/transform.go
+++ b/internal/maps/transform.go
@@ -3,18 +3,22 @@
 
 package maps
 
-func TransformKeys(src map[string]interface{}, keyMap func(string) string) {
+func TransformKeys(src map[string]interface{}, keyMap func(string) string, mapKeyCaseSensitive bool) {
 	if src == nil || keyMap == nil {
 		return
 	}
 	for key, value := range src {
 		if m, ok := value.(map[string]interface{}); ok {
-			TransformKeys(m, keyMap)
+			TransformKeys(m, keyMap, mapKeyCaseSensitive)
 		}
 		newKey := keyMap(key)
 		if newKey != key {
 			delete(src, key)
-			src[newKey] = Pack(key, value)
+			if mapKeyCaseSensitive {
+				src[newKey] = Pack(key, value)
+			} else {
+				src[newKey] = value
+			}
 		}
 	}
 }
diff --git a/internal/maps/transform_test.go b/internal/maps/transform_test.go
index e3120f3a..f70ffbb9 100644
--- a/internal/maps/transform_test.go
+++ b/internal/maps/transform_test.go
@@ -15,10 +15,11 @@ func TestTransformKeys(t *testing.T) {
 	t.Parallel()
 
 	testcases := []struct {
-		description string
-		src         map[string]any
-		keyMap      func(string) string
-		expected    map[string]any
+		description         string
+		src                 map[string]any
+		keyMap              func(string) string
+		mapKeyCaseSensitive bool
+		expected            map[string]any
 	}{
 		{
 			description: "nil map",
@@ -33,7 +34,14 @@ func TestTransformKeys(t *testing.T) {
 			description: "transform keys",
 			src:         map[string]any{"A": map[string]any{"X": 1, "y": 2}},
 			keyMap:      strings.ToLower,
-			expected:    map[string]any{"a": maps.Pack("A", map[string]any{"x": maps.Pack("X", 1), "y": 2})},
+			expected:    map[string]any{"a": map[string]any{"x": 1, "y": 2}},
+		},
+		{
+			description:         "transform keys",
+			src:                 map[string]any{"A": map[string]any{"X": 1, "y": 2}},
+			keyMap:              strings.ToLower,
+			mapKeyCaseSensitive: true,
+			expected:            map[string]any{"a": maps.Pack("A", map[string]any{"x": maps.Pack("X", 1), "y": 2})},
 		},
 	}
 
@@ -42,7 +50,7 @@ func TestTransformKeys(t *testing.T) {
 		t.Run(tc.description, func(t *testing.T) {
 			t.Parallel()
 
-			maps.TransformKeys(tc.src, tc.keyMap)
+			maps.TransformKeys(tc.src, tc.keyMap, tc.mapKeyCaseSensitive)
 			assert.Equal(t, tc.expected, tc.src)
 		})
 	}
diff --git a/option.go b/option.go
index b0c135bf..a532f3f4 100644
--- a/option.go
+++ b/option.go
@@ -68,6 +68,13 @@ func WithCaseSensitive() Option {
 	}
 }
 
+// WithMapKeyCaseSensitive enables the case sensitivity of the map keys.
+func WithMapKeyCaseSensitive() Option {
+	return func(options *options) {
+		options.mapKeyCaseSensitive = true
+	}
+}
+
 type (
 	// Option configures a Config with specific options.
 	Option  func(*options)