diff --git a/scm-webapp/src/main/java/sonia/scm/security/AnonymousRealm.java b/scm-webapp/src/main/java/sonia/scm/security/AnonymousRealm.java
index 17a14cce73..16ecead815 100644
--- a/scm-webapp/src/main/java/sonia/scm/security/AnonymousRealm.java
+++ b/scm-webapp/src/main/java/sonia/scm/security/AnonymousRealm.java
@@ -6,8 +6,10 @@ import org.apache.shiro.authc.AuthenticationInfo;
 import org.apache.shiro.authc.AuthenticationToken;
 import org.apache.shiro.authc.credential.AllowAllCredentialsMatcher;
 import org.apache.shiro.realm.AuthenticatingRealm;
+import sonia.scm.ConfigurationException;
 import sonia.scm.SCMContext;
 import sonia.scm.plugin.Extension;
+import sonia.scm.user.UserDAO;
 
 import javax.inject.Singleton;
 
@@ -27,10 +29,12 @@ public class AnonymousRealm extends AuthenticatingRealm {
    * dao realm helper
    */
   private final DAORealmHelper helper;
+  private final UserDAO userDAO;
 
   @Inject
-  public AnonymousRealm(DAORealmHelperFactory helperFactory) {
+  public AnonymousRealm(DAORealmHelperFactory helperFactory, UserDAO userDAO) {
     this.helper = helperFactory.create(REALM);
+    this.userDAO = userDAO;
 
     setAuthenticationTokenClass(AnonymousToken.class);
     setCredentialsMatcher(new AllowAllCredentialsMatcher());
@@ -38,6 +42,9 @@ public class AnonymousRealm extends AuthenticatingRealm {
 
   @Override
   protected AuthenticationInfo doGetAuthenticationInfo(AuthenticationToken authenticationToken) {
+    if (!userDAO.contains(SCMContext.USER_ANONYMOUS)) {
+     throw new ConfigurationException("trying to access anonymous but _anonymous user does not exist");
+    }
     checkArgument(authenticationToken instanceof AnonymousToken, "%s is required", AnonymousToken.class);
     return helper.authenticationInfoBuilder(SCMContext.USER_ANONYMOUS).build();
   }
diff --git a/scm-webapp/src/test/java/sonia/scm/security/AnonymousRealmTest.java b/scm-webapp/src/test/java/sonia/scm/security/AnonymousRealmTest.java
index 769d7406ca..1a67ea192c 100644
--- a/scm-webapp/src/test/java/sonia/scm/security/AnonymousRealmTest.java
+++ b/scm-webapp/src/test/java/sonia/scm/security/AnonymousRealmTest.java
@@ -8,7 +8,9 @@ import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.InjectMocks;
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
+import sonia.scm.ConfigurationException;
 import sonia.scm.SCMContext;
+import sonia.scm.user.UserDAO;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -26,6 +28,9 @@ class AnonymousRealmTest {
   @Mock
   private DAORealmHelper.AuthenticationInfoBuilder builder;
 
+  @Mock
+  private UserDAO userDAO;
+
   @InjectMocks
   private AnonymousRealm realm;
 
@@ -35,20 +40,28 @@ class AnonymousRealmTest {
   @BeforeEach
   void prepareObjectUnderTest() {
     when(realmHelperFactory.create(AnonymousRealm.REALM)).thenReturn(realmHelper);
-    realm = new AnonymousRealm(realmHelperFactory);
+    realm = new AnonymousRealm(realmHelperFactory, userDAO);
   }
 
   @Test
   void shouldDoGetAuthentication() {
     when(realmHelper.authenticationInfoBuilder(SCMContext.USER_ANONYMOUS)).thenReturn(builder);
     when(builder.build()).thenReturn(authenticationInfo);
+    when(userDAO.contains(SCMContext.USER_ANONYMOUS)).thenReturn(true);
 
     AuthenticationInfo result = realm.doGetAuthenticationInfo(new AnonymousToken());
     assertThat(result).isSameAs(authenticationInfo);
   }
 
+  @Test
+  void shouldThrowNotAuthorizedExceptionIfAnonymousUserNotExists() {
+    when(userDAO.contains(SCMContext.USER_ANONYMOUS)).thenReturn(false);
+    assertThrows(ConfigurationException.class, () -> realm.doGetAuthenticationInfo(new AnonymousToken()));
+  }
+
   @Test
   void shouldThrowIllegalArgumentExceptionForWrongTypeOfToken() {
+    when(userDAO.contains(SCMContext.USER_ANONYMOUS)).thenReturn(true);
     assertThrows(IllegalArgumentException.class, () -> realm.doGetAuthenticationInfo(new UsernamePasswordToken()));
   }
 }