diff --git a/pkg/miniauth/error.go b/pkg/miniauth/error.go
index 79d6f9b..d7f428b 100644
--- a/pkg/miniauth/error.go
+++ b/pkg/miniauth/error.go
@@ -3,6 +3,6 @@ package miniauth
 import "errors"
 
 var (
-	ErrUSernameInvalide     = errors.New("username not valide")
 	ErrUserHasInvalideChars = errors.New("username has invalide chars")
+	ErrUsernameIsTaken      = errors.New("username already takebn")
 )
diff --git a/pkg/miniauth/miniauth.go b/pkg/miniauth/miniauth.go
index 11d99cd..2bda06a 100644
--- a/pkg/miniauth/miniauth.go
+++ b/pkg/miniauth/miniauth.go
@@ -34,5 +34,15 @@ func (m Miniauth) checkUsernameForRegistration(username string) error {
 	if !reg.MatchString(username) {
 		return ErrUserHasInvalideChars
 	}
+
+	exists, err := m.store.UserExists(username)
+	if err != nil {
+		return err
+	}
+
+	if exists {
+		return ErrUsernameIsTaken
+	}
+
 	return nil
 }
diff --git a/pkg/miniauth/miniauth_test.go b/pkg/miniauth/miniauth_test.go
index 897824f..df156cb 100644
--- a/pkg/miniauth/miniauth_test.go
+++ b/pkg/miniauth/miniauth_test.go
@@ -38,9 +38,16 @@ func TestInvalideUsernames(t *testing.T) {
 			username: "kekskurse",
 			exptErr:  nil,
 		},
+		{
+			name:     "username already taken",
+			username: "testuser",
+			exptErr:  ErrUsernameIsTaken,
+		},
 	}
 
 	ma := getMiniAuth(t)
+	_, err := ma.store.UserWrite("testuser", "testpassword")
+	assert.Nil(t, err, "[setup] should be abel to write user without error")
 	for _, tt := range tts {
 		t.Run(tt.name, func(t *testing.T) {
 			err := ma.checkUsernameForRegistration(tt.username)
diff --git a/pkg/userstore/users.go b/pkg/userstore/users.go
index 513ae21..6a07cb2 100644
--- a/pkg/userstore/users.go
+++ b/pkg/userstore/users.go
@@ -7,7 +7,7 @@ import (
 
 func (s Store) UserWrite(username, password string) (int64, error) {
 	query := "INSERT INTO users (username, password) VALUES (?, ?);"
-	log := s.log.With().Str("query", query).Str("username", username).Logger()
+	log := s.log.With().Str("func", "UserWrite").Str("query", query).Str("username", username).Logger()
 
 	pwHash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
 	if err != nil {
@@ -25,3 +25,20 @@ func (s Store) UserWrite(username, password string) (int64, error) {
 	}
 	return id, nil
 }
+
+func (s Store) UserExists(username string) (bool, error) {
+	query := "SELECT COUNT(*) FROM users WHERE username = ?"
+	log := s.log.With().Str("func", "UserExists").Str("query", query).Str("username", username).Logger()
+
+	var count int
+	err := s.db.QueryRow(query, username).Scan(&count)
+	if err != nil {
+		return true, utils.WrapError(ErrCantExecuteQuery, err, log)
+	}
+
+	if count == 0 {
+		return false, nil
+	}
+
+	return true, nil
+}
diff --git a/pkg/userstore/users_test.go b/pkg/userstore/users_test.go
index 64515ce..267548f 100644
--- a/pkg/userstore/users_test.go
+++ b/pkg/userstore/users_test.go
@@ -68,3 +68,19 @@ func TestWriteUser(t *testing.T) {
 	assert.NotEqual(t, "kekskurse", pw2)
 	assert.NotEqual(t, pw1, pw2, "passwords should not be equal")
 }
+
+func TestUserExists(t *testing.T) {
+	store, err := NewDummyStore()
+	assert.Nil(t, err, "[setup] should get dummy store without error")
+
+	exists, err := store.UserExists("kekskurse")
+	assert.Nil(t, err)
+	assert.False(t, exists)
+
+	_, err = store.UserWrite("kekskurse", "kekskurse")
+	assert.Nil(t, err, "[setup] should be abel to create user")
+
+	exists, err = store.UserExists("kekskurse")
+	assert.Nil(t, err)
+	assert.True(t, exists)
+}