diff --git a/resources/qml/InviteDialog.qml b/resources/qml/InviteDialog.qml
index 002a35c2..9ace3246 100644
--- a/resources/qml/InviteDialog.qml
+++ b/resources/qml/InviteDialog.qml
@@ -16,6 +16,10 @@ ApplicationWindow {
             invitees.addUser(inviteeEntry.text);
             inviteeEntry.clear();
         }
+        else
+        {
+            warningLabel.show()
+        }
     }
 
     title: qsTr("Invite users to ") + roomName
@@ -51,6 +55,11 @@ ApplicationWindow {
                 Layout.fillWidth: true
                 onAccepted: if (text !== "") addInvite()
                 Component.onCompleted: forceActiveFocus()
+
+                Shortcut {
+                    sequence: "Ctrl+Enter"
+                    onActivated: inviteDialogRoot.accept()
+                }
             }
 
             Button {
@@ -59,6 +68,70 @@ ApplicationWindow {
             }
         }
 
+        Label {
+            id: warningLabel
+
+            function show() {
+                state = "shown";
+                warningLabelTimer.start();
+            }
+
+            text: qsTr("Please enter a valid username (e.g. @joe:matrix.org).")
+            color: "red"
+            visible: false
+            opacity: 0
+            state: "hidden"
+
+            states: [
+                State {
+                    name: "shown"
+                    PropertyChanges {
+                        target: warningLabel
+                        opacity: 1
+                        visible: true
+                    }
+                },
+                State {
+                    name: "hidden"
+                    PropertyChanges {
+                        target: warningLabel
+                        opacity: 0
+                        visible: false
+                    }
+                }
+            ]
+
+            transitions: [
+                Transition {
+                    from: "shown"
+                    to: "hidden"
+                    reversible: true
+
+                    SequentialAnimation {
+                        NumberAnimation {
+                            target: warningLabel
+                            property: "opacity"
+                            duration: 500
+                        }
+
+                        PropertyAction {
+                            target: warningLabel
+                            property: "visible"
+                        }
+                    }
+                }
+            ]
+
+            Timer {
+                id: warningLabelTimer
+
+                interval: 2000
+                repeat: false
+                running: false
+                onTriggered: warningLabel.state = "hidden"
+            }
+        }
+
         ListView {
             id: inviteesList