diff --git a/lumi2/static/js/group_edit.js b/lumi2/static/js/group_edit.js
index 88ddddc..a80ffdb 100644
--- a/lumi2/static/js/group_edit.js
+++ b/lumi2/static/js/group_edit.js
@@ -26,11 +26,10 @@ class UserEntry {
             $(this.userEntry.buttonElement).click(() => this.userEntry.onClickJoin());
             $(this.userEntry.rowElement).prependTo($("#tableNonMembers").find("tbody"));
             this.userEntry.setButtonAppearanceJoinGroup();
-            // TODO check status code!
         }).fail(function(xhr, status, errorThrown) {
             console.log(`Error: ${errorThrown}`);
             console.log(`Status: ${status}`);
-            alert("Sorry, there was a problem retrieving information from the server.");
+            showErrorMessage(xhr.responseJSON['message']);
             this.userEntry.setButtonAppearanceLeaveGroup();
         });
     }
@@ -50,12 +49,11 @@ class UserEntry {
             $(this.userEntry.buttonElement).click(() => this.userEntry.onClickLeave());
             $(this.userEntry.rowElement).prependTo($("#tableMembers").find("tbody"));
             this.userEntry.setButtonAppearanceLeaveGroup();
-            // TODO check status code!
         }).fail(function(xhr, status, errorThrown) {
             console.log(`Error: ${errorThrown}`);
             console.log(`Status: ${status}`);
-            alert("Sorry, there was a problem retrieving information from the server.");
-            this.userEntry.setButtonAppearanceLeaveGroup();
+            showErrorMessage(xhr.responseJSON['message']);
+            this.userEntry.setButtonAppearanceJoinGroup();
         });
     }
 
@@ -88,6 +86,15 @@ class UserEntry {
     }
 }
 
+function showErrorMessage(message) {
+    $("nav").after([
+    '<div class="alert alert-danger alert-dismissible" role="alert">',
+        `<div>${message}</div>`,
+        '<button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>',
+    '</div>'
+    ].join(''));
+}
+
 function getUserEntries() {
     let userEntries = [];
 
diff --git a/lumi2/templates/base.html b/lumi2/templates/base.html
index 406e032..3c6f8fa 100644
--- a/lumi2/templates/base.html
+++ b/lumi2/templates/base.html
@@ -57,7 +57,10 @@
         {% with messages = get_flashed_messages() %}
         {% if messages %}
         {% for message in messages %}
-        <div class="alert alert-primary mt-3">{{ message }}</div>
+        <div class="alert alert-primary alert-dismissible" role="alert">
+            <div>{{ message }}</div>
+            <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
+        </div>
         {% endfor %}
         {% endif %}
         {% endwith %}
diff --git a/lumi2/webapi.py b/lumi2/webapi.py
index ce41ead..8c0e50e 100644
--- a/lumi2/webapi.py
+++ b/lumi2/webapi.py
@@ -283,6 +283,14 @@ class GroupMemberResource(Resource):
             conn.unbind()
             return {"message": f"User '{username}' is not a member of the Group '{group.groupname}'."}, 400
 
+        if len(group.members) == 1:
+            conn.unbind()
+            return {
+                "message": f"Cannot remove user '{username}', because they are currently the only member " \
+                           f"of '{group.groupname}'. Empty groups are not permitted in LDAP, so either " \
+                           f"delete the group or add another user before removing '{username}'."
+            }, 400
+
         group.members.remove(user)
         ldap.update_group(conn, group)
         conn.unbind()