diff --git a/rhodecode/api/tests/test_grant_user_group_permission.py b/rhodecode/api/tests/test_grant_user_group_permission.py
--- a/rhodecode/api/tests/test_grant_user_group_permission.py
+++ b/rhodecode/api/tests/test_grant_user_group_permission.py
@@ -66,7 +66,7 @@ class TestGrantUserGroupPermission(objec
             perm=perm)
         response = api_call(self.app, params)
 
-        expected = 'permission `%s` does not exist' % (perm,)
+        expected = 'permission `%s` does not exist.' % (perm,)
         assert_error(id_, expected, given=response.body)
 
     @mock.patch.object(RepoModel, 'grant_user_group_permission', crash)
diff --git a/rhodecode/api/tests/test_grant_user_group_permission_to_repo_group.py b/rhodecode/api/tests/test_grant_user_group_permission_to_repo_group.py
--- a/rhodecode/api/tests/test_grant_user_group_permission_to_repo_group.py
+++ b/rhodecode/api/tests/test_grant_user_group_permission_to_repo_group.py
@@ -132,8 +132,7 @@ class TestGrantUserGroupPermissionFromRe
                 RepoGroupModel().revoke_user_group_permission(
                     repo_group.group_id, user_group.users_group_id)
         else:
-            expected = 'repository group `%s` does not exist' % (
-                repo_group.name,)
+            expected = 'repository group `%s` does not exist' % (repo_group.name,)
             assert_error(id_, expected, given=response.body)
 
     def test_api_grant_user_group_permission_to_repo_group_wrong_permission(
@@ -149,7 +148,7 @@ class TestGrantUserGroupPermissionFromRe
             perm=perm)
         response = api_call(self.app, params)
 
-        expected = 'permission `%s` does not exist' % (perm,)
+        expected = 'permission `%s` does not exist. Permission should start with prefix: `group.`' % (perm,)
         assert_error(id_, expected, given=response.body)
 
     @mock.patch.object(RepoGroupModel, 'grant_user_group_permission', crash)
diff --git a/rhodecode/api/tests/test_grant_user_permission.py b/rhodecode/api/tests/test_grant_user_permission.py
--- a/rhodecode/api/tests/test_grant_user_permission.py
+++ b/rhodecode/api/tests/test_grant_user_permission.py
@@ -65,7 +65,7 @@ class TestGrantUserPermission(object):
             perm=perm)
         response = api_call(self.app, params)
 
-        expected = 'permission `%s` does not exist' % (perm,)
+        expected = 'permission `%s` does not exist.' % (perm,)
         assert_error(id_, expected, given=response.body)
 
     @mock.patch.object(RepoModel, 'grant_user_permission', crash)
diff --git a/rhodecode/api/tests/test_grant_user_permission_to_repo_group.py b/rhodecode/api/tests/test_grant_user_permission_to_repo_group.py
--- a/rhodecode/api/tests/test_grant_user_permission_to_repo_group.py
+++ b/rhodecode/api/tests/test_grant_user_permission_to_repo_group.py
@@ -132,7 +132,7 @@ class TestGrantUserPermissionFromRepoGro
             perm=perm)
         response = api_call(self.app, params)
 
-        expected = 'permission `%s` does not exist' % (perm,)
+        expected = 'permission `%s` does not exist. Permission should start with prefix: `group.`' % (perm,)
         assert_error(id_, expected, given=response.body)
 
     @mock.patch.object(RepoGroupModel, 'grant_user_permission', crash)
diff --git a/rhodecode/api/tests/test_grant_user_permission_to_user_group.py b/rhodecode/api/tests/test_grant_user_permission_to_user_group.py
--- a/rhodecode/api/tests/test_grant_user_permission_to_user_group.py
+++ b/rhodecode/api/tests/test_grant_user_permission_to_user_group.py
@@ -130,7 +130,7 @@ class TestGrantUserPermissionFromUserGro
             perm=perm)
         response = api_call(self.app, params)
 
-        expected = 'permission `%s` does not exist' % perm
+        expected = 'permission `%s` does not exist. Permission should start with prefix: `usergroup.`' % perm
         assert_error(id_, expected, given=response.body)
 
     def test_api_grant_user_permission_to_user_group_exception_when_adding(
diff --git a/rhodecode/api/utils.py b/rhodecode/api/utils.py
--- a/rhodecode/api/utils.py
+++ b/rhodecode/api/utils.py
@@ -308,7 +308,11 @@ def get_perm_or_error(permid, prefix=Non
 
     perm = PermissionModel.cls.get_by_key(permid)
     if perm is None:
-        raise JSONRPCError('permission `%s` does not exist' % (permid,))
+        msg = 'permission `{}` does not exist.'.format(permid)
+        if prefix:
+            msg += ' Permission should start with prefix: `{}`'.format(prefix)
+        raise JSONRPCError(msg)
+
     if prefix:
         if not perm.permission_name.startswith(prefix):
             raise JSONRPCError('permission `%s` is invalid, '