diff --git a/README.md b/README.md
index c860ee0..2ab37d3 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ Confita is a library that loads configuration from multiple backends and stores
 ## Install
 
 ```sh
-go get -u github.com/heetch/confita
+go get -u github.com/karantin2020/confita
 ```
 
 ## Usage
@@ -95,7 +95,10 @@ A loader can take other configured backends as parameters.
 
 ```go
 loader := confita.NewLoader(
-  env.NewBackend(),
+  env.NewBackend(
+    env.WithPrefix("PREFIX"),
+		env.ToUpper(),
+  ),
   file.NewBackend("/path/to/config.json"),
   file.NewBackend("/path/to/config.yaml"),
   flags.NewBackend(),
@@ -124,7 +127,6 @@ err := loader.Load(ctx, &cfg)
 If a key is not found, Confita won't change the respective struct field. With that in mind, default values can simply be implemented by filling the structure before passing it to Confita.
 
 ```go
-
 type Config struct {
   Host        string        `config:"host"`
   Port        uint32        `config:"port"`
diff --git a/backend/env/env.go b/backend/env/env.go
index 94b024f..28ed6bf 100644
--- a/backend/env/env.go
+++ b/backend/env/env.go
@@ -11,20 +11,43 @@ import (
 // NewBackend creates a configuration loader that loads from the environment.
 // If the key is not found, this backend tries again by turning any kebabcase key to snakecase and
 // lowercase letters to uppercase.
-func NewBackend() backend.Backend {
+func NewBackend(fns ...opt) backend.Backend {
 	return backend.Func("env", func(ctx context.Context, key string) ([]byte, error) {
-		val, ok := os.LookupEnv(key)
+		key = strings.Replace(key, "-", "_", -1)
+		val, ok := os.LookupEnv(opts(key, fns...))
 		if ok {
 			return []byte(val), nil
 		}
-
-		key = strings.Replace(strings.ToUpper(key), "-", "_", -1)
-
-		val, ok = os.LookupEnv(key)
+		val, ok = os.LookupEnv(opts(strings.ToUpper(key), fns...))
 		if ok {
 			return []byte(val), nil
 		}
-
 		return nil, backend.ErrNotFound
 	})
 }
+
+// WithPrefix adds preffix for searching env variable
+func WithPrefix(preffix string) opt {
+	if !strings.HasSuffix(preffix, "_") {
+		preffix = preffix + "_"
+	}
+	return func(key string) string {
+		return preffix + key
+	}
+}
+
+// ToUpper uppercases searching env variable
+func ToUpper() opt {
+	return func(key string) string {
+		return strings.ToUpper(key)
+	}
+}
+
+type opt func(key string) string
+
+func opts(key string, fns ...opt) string {
+	for i := range fns {
+		key = fns[i](key)
+	}
+	return key
+}
diff --git a/backend/env/env_test.go b/backend/env/env_test.go
index 904f8b7..85720b3 100644
--- a/backend/env/env_test.go
+++ b/backend/env/env_test.go
@@ -3,6 +3,7 @@ package env
 import (
 	"context"
 	"os"
+	"reflect"
 	"testing"
 
 	"github.com/heetch/confita/backend"
@@ -35,3 +36,99 @@ func TestEnvBackend(t *testing.T) {
 		require.Equal(t, "ok", string(val))
 	})
 }
+
+func TestOpts(t *testing.T) {
+	type args struct {
+		fns []opt
+		key string
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{
+			name: "Test opts positive",
+			args: args{
+				fns: []opt{
+					ToUpper(),
+					WithPrefix("TEST_"),
+				},
+				key: "var",
+			},
+			want: "TEST_VAR",
+		},
+		{
+			name: "Test upper after prefix with lower key",
+			args: args{
+				fns: []opt{
+					WithPrefix("test"),
+					ToUpper(),
+				},
+				key: "var",
+			},
+			want: "TEST_VAR",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := opts(tt.args.key, tt.args.fns...); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("NewBackend() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestWithPrefix(t *testing.T) {
+	type args struct {
+		preffix string
+		key     string
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{
+			name: "Test add preffix positive",
+			args: args{
+				preffix: "TEST",
+				key:     "VAR",
+			},
+			want: "TEST_VAR",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := WithPrefix(tt.args.preffix)(tt.args.key); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("WithPrefix() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestToUpper(t *testing.T) {
+	type args struct {
+		key string
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{
+			name: "Test add preffix positive",
+			args: args{
+				"test",
+			},
+			want: "TEST",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := ToUpper()(tt.args.key); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("ToUpper() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}