diff --git a/app/src/main/java/de/sebse/fuplanner/MainActivity.java b/app/src/main/java/de/sebse/fuplanner/MainActivity.java
index f379311..a0aa3e5 100644
--- a/app/src/main/java/de/sebse/fuplanner/MainActivity.java
+++ b/app/src/main/java/de/sebse/fuplanner/MainActivity.java
@@ -6,6 +6,7 @@ import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
 import android.widget.TextView;
+import android.widget.Toast;
 
 import com.google.android.material.navigation.NavigationView;
 
@@ -476,36 +477,54 @@ public class MainActivity extends AppCompatActivity
         toLoginState(loginToken.getFullname(), loginToken.getEmail(), getDefaultFragmentAfterLogin(), "", onlineMode);
     }
 
+    @Override
     public void onModulesFragmentInteraction(final String itemID) {
         changeFragment(FRAGMENT_MODULES_DETAILS, itemID);
     }
 
+    @Override
     public void onCanteensFragmentInteraction(final int itemID) {
         changeFragment(FRAGMENT_CANTEENS_DETAILS, String.valueOf(itemID));
     }
 
+    @Override
     public void onTitleTextChange(String newTitle) {
         setTitle(newTitle);
     }
 
+    @Override
     public void onTitleTextChange(@StringRes int titleId) {
         setTitle(titleId);
     }
 
+    @Override
     public void loginTokenInvalid(boolean doPrecheck) {
         getKVV().invalidate();
         checkAndDoLogin();
     }
 
+    @Override
     public void refreshFailed(boolean isFailed) {
         setRefreshFailedBanner(isFailed);
     }
 
+    @Override
     public void addRequestPermissionsResultListener(RequestPermissionsResultListener listener, String id) {
         permissionListeners.put(id, listener);
     }
 
+    @Override
     public void removeRequestPermissionsResultListener(String id) {
         permissionListeners.remove(id);
     }
+
+    @Override
+    public void showToast(@StringRes int msgStringRes) {
+        showToast(getString(msgStringRes));
+    }
+
+    @Override
+    public void showToast(String message) {
+        Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
+    }
 }
diff --git a/app/src/main/java/de/sebse/fuplanner/fragments/LoginFragment.java b/app/src/main/java/de/sebse/fuplanner/fragments/LoginFragment.java
index 30ee62a..6471594 100644
--- a/app/src/main/java/de/sebse/fuplanner/fragments/LoginFragment.java
+++ b/app/src/main/java/de/sebse/fuplanner/fragments/LoginFragment.java
@@ -33,6 +33,7 @@ import de.sebse.fuplanner.tools.logging.Logger;
 public class LoginFragment extends Fragment {
     private OnLoginFragmentInteractionListener mListener;
     private final Logger log = new Logger(this);
+    private MainActivityListener mActivityListener;
 
     public LoginFragment() {
         // Required empty public constructor
@@ -96,10 +97,20 @@ public class LoginFragment extends Fragment {
                     kvv.login(username, password, success -> {
                         progressDialog.dismiss();
                         gauth.setLoginState(username, password);
-                        if (mListener != null)
+                        if (mListener != null) {
+                            input_usr.setError(null);
+                            input_pwd.setError(null);
                             mListener.onLoginFragmentInteraction(success, true);
+                        }
                     }, error -> {
                         progressDialog.dismiss();
+                        // Invalid password
+                        if (error.getCode() == 100131 && mActivityListener != null) {
+                            mActivityListener.showToast(R.string.invalid_credentials);
+                            input_usr.setError(input_usr.getResources().getString(R.string.invalid_credentials));
+                            input_pwd.setError(input_pwd.getResources().getString(R.string.invalid_credentials));
+                        } else
+                            mActivityListener.showToast(v.getResources().getString(R.string.error_occurred_code, error.getCode()));
                         log.e("Error on KVV login!", error);
                     });
                 }
@@ -120,9 +131,10 @@ public class LoginFragment extends Fragment {
             throw new RuntimeException(context.toString()
                     + " must implement OnLoginFragmentInteractionListener");
         }
-        if (context instanceof MainActivityListener)
-            ((MainActivityListener) context).onTitleTextChange(R.string.log_in);
-        else
+        if (context instanceof MainActivityListener) {
+            mActivityListener = (MainActivityListener) context;
+            mActivityListener.onTitleTextChange(R.string.log_in);
+        } else
             throw new RuntimeException(context.toString() + "must implement MainActivityListener");
     }
 
diff --git a/app/src/main/java/de/sebse/fuplanner/tools/MainActivityListener.java b/app/src/main/java/de/sebse/fuplanner/tools/MainActivityListener.java
index 3efe281..6e2cfb1 100644
--- a/app/src/main/java/de/sebse/fuplanner/tools/MainActivityListener.java
+++ b/app/src/main/java/de/sebse/fuplanner/tools/MainActivityListener.java
@@ -24,4 +24,8 @@ public interface MainActivityListener {
     void addRequestPermissionsResultListener(RequestPermissionsResultListener listener, String id);
 
     void removeRequestPermissionsResultListener(String id);
+
+    void showToast(@StringRes int msgStringRes);
+
+    void showToast(String message);
 }
diff --git a/app/src/main/res/values-de/strings.xml b/app/src/main/res/values-de/strings.xml
index acd5e32..1014709 100644
--- a/app/src/main/res/values-de/strings.xml
+++ b/app/src/main/res/values-de/strings.xml
@@ -61,4 +61,6 @@
     <string name="openFile">Datei Öffnen</string>
     <string name="ErrorFileDownload">Download-Fehler</string>
     <string name="ErrorFileDownloadText">Beim Herunterladen der Datei ist ein Fehler aufgetreten. Prüfe, ob Du mit dem Internet verbunden bist und der App Zugriff auf den Speicher gewährt hast.</string>
+    <string name="invalid_credentials">Ungültiger Benutzername oder Password!</string>
+    <string name="error_occurred_code">Fehler %1$d aufgetreten!</string>
 </resources>
\ No newline at end of file
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 04e4a3d..cb4f7b2 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -68,4 +68,6 @@
     <string name="openFile">Open File</string>
     <string name="ErrorFileDownload">Download Error</string>
     <string name="ErrorFileDownloadText">An error occurred while downloading the file. Please check if you are connected to the internet and if you have granted storage access to the app.</string>
+    <string name="invalid_credentials">Invalid username or password!</string>
+    <string name="error_occurred_code">Error occurred: %1$d</string>
 </resources>