diff --git a/middlewares/authenticate.go b/middlewares/authenticate.go
index ade864c..4298795 100644
--- a/middlewares/authenticate.go
+++ b/middlewares/authenticate.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"github.com/muety/wakapi/utils"
+	"log"
 	"net/http"
 	"strings"
 	"time"
@@ -94,18 +95,33 @@ func (m *AuthenticateMiddleware) tryGetUserByCookie(r *http.Request) (*models.Us
 		return nil, err
 	}
 
-	var user *models.User
 	cachedUser, ok := m.cache.Get(login.Username)
-	if !ok {
-		user, err = m.userSrvc.GetUserById(login.Username)
-		if err != nil {
-			return nil, err
-		}
-		if !utils.CheckPassword(user, login.Password, m.config.PasswordSalt) {
-			return nil, errors.New("invalid password")
-		}
-	} else {
-		user = cachedUser.(*models.User)
+
+	if ok {
+		return cachedUser.(*models.User), nil
 	}
+
+	user, err := m.userSrvc.GetUserById(login.Username)
+	if err != nil {
+		return nil, err
+	}
+
+	if !CheckAndMigratePassword(user, login, m.config.PasswordSalt, m.userSrvc) {
+		return nil, errors.New("invalid password")
+	}
+
 	return user, nil
 }
+
+// migrate old md5-hashed passwords to new salted bcrypt hashes for backwards compatibility
+func CheckAndMigratePassword(user *models.User, login *models.Login, salt string, userServiceRef *services.UserService) bool {
+	if utils.IsMd5(user.Password) {
+		if utils.CheckPasswordMd5(user, login.Password) {
+			log.Printf("migrating old md5 password to new bcrypt format for user '%s'", user.ID)
+			userServiceRef.MigrateMd5Password(user, login)
+			return true
+		}
+		return false
+	}
+	return utils.CheckPasswordBcrypt(user, login.Password, salt)
+}
diff --git a/routes/public.go b/routes/public.go
index f4b5fc7..9c7a5ce 100644
--- a/routes/public.go
+++ b/routes/public.go
@@ -3,6 +3,7 @@ package routes
 import (
 	"fmt"
 	"github.com/gorilla/schema"
+	"github.com/muety/wakapi/middlewares"
 	"github.com/muety/wakapi/models"
 	"github.com/muety/wakapi/services"
 	"github.com/muety/wakapi/utils"
@@ -76,7 +77,8 @@ func (h *IndexHandler) Login(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if !utils.CheckPassword(user, login.Password, h.config.PasswordSalt) {
+	// TODO: depending on middleware package here is a hack
+	if !middlewares.CheckAndMigratePassword(user, &login, h.config.PasswordSalt, h.userSrvc) {
 		respondAlert(w, "invalid credentials", "", "", http.StatusUnauthorized)
 		return
 	}
diff --git a/services/user.go b/services/user.go
index 749340c..81768a8 100644
--- a/services/user.go
+++ b/services/user.go
@@ -1,6 +1,7 @@
 package services
 
 import (
+	"errors"
 	"github.com/jinzhu/gorm"
 	"github.com/muety/wakapi/models"
 	"github.com/muety/wakapi/utils"
@@ -67,3 +68,19 @@ func (srv *UserService) CreateOrGet(signup *models.Signup) (*models.User, bool,
 
 	return u, false, nil
 }
+
+func (srv *UserService) MigrateMd5Password(user *models.User, login *models.Login) (*models.User, error) {
+	user.Password = login.Password
+	if err := utils.HashPassword(user, srv.Config.PasswordSalt); err != nil {
+		return nil, err
+	}
+
+	result := srv.Db.Model(user).Update("password", user.Password)
+	if err := result.Error; err != nil {
+		return nil, err
+	} else if result.RowsAffected < 1 {
+		return nil, errors.New("nothing changes")
+	}
+
+	return user, nil
+}
diff --git a/utils/auth.go b/utils/auth.go
index d47aaea..0721bbf 100644
--- a/utils/auth.go
+++ b/utils/auth.go
@@ -1,7 +1,9 @@
 package utils
 
 import (
+	"crypto/md5"
 	"encoding/base64"
+	"encoding/hex"
 	"errors"
 	"github.com/muety/wakapi/models"
 	"golang.org/x/crypto/bcrypt"
@@ -10,6 +12,8 @@ import (
 	"strings"
 )
 
+var md5Regex = regexp.MustCompile(`^[a-f0-9]{32}$`)
+
 func ExtractBasicAuth(r *http.Request) (username, password string, err error) {
 	authHeader := strings.Split(r.Header.Get("Authorization"), " ")
 	if len(authHeader) != 2 || authHeader[0] != "Basic" {
@@ -54,11 +58,25 @@ func ExtractCookieAuth(r *http.Request, config *models.Config) (login *models.Lo
 	return login, nil
 }
 
-func CheckPassword(user *models.User, password, salt string) bool {
+func IsMd5(hash string) bool {
+	return md5Regex.Match([]byte(hash))
+}
+
+func CheckPasswordBcrypt(user *models.User, password, salt string) bool {
 	err := bcrypt.CompareHashAndPassword([]byte(user.Password), []byte(password+salt))
 	return err == nil
 }
 
+// deprecated, only here for backwards compatibility
+func CheckPasswordMd5(user *models.User, password string) bool {
+	hash := md5.Sum([]byte(password))
+	hashStr := hex.EncodeToString(hash[:])
+	if hashStr == user.Password {
+		return true
+	}
+	return false
+}
+
 // inplace
 func HashPassword(u *models.User, salt string) error {
 	bytes, err := bcrypt.GenerateFromPassword([]byte(u.Password+salt), bcrypt.DefaultCost)
diff --git a/version.txt b/version.txt
index 3e1ad72..8e03717 100644
--- a/version.txt
+++ b/version.txt
@@ -1 +1 @@
-1.5.0
\ No newline at end of file
+1.5.1
\ No newline at end of file