diff --git a/src/components/views/dialogs/TextInputDialog.js b/src/components/views/dialogs/TextInputDialog.js
index 4b21e8206e..e56e9f2b87 100644
--- a/src/components/views/dialogs/TextInputDialog.js
+++ b/src/components/views/dialogs/TextInputDialog.js
@@ -18,6 +18,7 @@ import React, {createRef} from 'react';
 import createReactClass from 'create-react-class';
 import PropTypes from 'prop-types';
 import * as sdk from '../../../index';
+import Field from "../elements/Field";
 
 export default createReactClass({
     displayName: 'TextInputDialog',
@@ -33,6 +34,7 @@ export default createReactClass({
         focus: PropTypes.bool,
         onFinished: PropTypes.func.isRequired,
         hasCancel: PropTypes.bool,
+        validator: PropTypes.func, // result of withValidation
     },
 
     getDefaultProps: function() {
@@ -45,25 +47,57 @@ export default createReactClass({
         };
     },
 
+    getInitialState: function() {
+        return {
+            value: this.props.value,
+            valid: false,
+        };
+    },
+
     UNSAFE_componentWillMount: function() {
-        this._textinput = createRef();
+        this._field = createRef();
     },
 
     componentDidMount: function() {
         if (this.props.focus) {
             // Set the cursor at the end of the text input
-            this._textinput.current.value = this.props.value;
+            // this._field.current.value = this.props.value;
+            this._field.current.focus();
         }
     },
 
-    onOk: function() {
-        this.props.onFinished(true, this._textinput.current.value);
+    onOk: async function(ev) {
+        ev.preventDefault();
+        if (this.props.validator) {
+            await this._field.current.validate({ allowEmpty: false });
+
+            if (!this._field.current.state.valid) {
+                this._field.current.focus();
+                this._field.current.validate({ allowEmpty: false, focused: true });
+                return;
+            }
+        }
+        this.props.onFinished(true, this.state.value);
     },
 
     onCancel: function() {
         this.props.onFinished(false);
     },
 
+    onChange: function(ev) {
+        this.setState({
+            value: ev.target.value,
+        });
+    },
+
+    onValidate: async function(fieldState) {
+        const result = await this.props.validator(fieldState);
+        this.setState({
+            valid: result.valid,
+        });
+        return result;
+    },
+
     render: function() {
         const BaseDialog = sdk.getComponent('views.dialogs.BaseDialog');
         const DialogButtons = sdk.getComponent('views.elements.DialogButtons');
@@ -77,14 +111,17 @@ export default createReactClass({
                             <label htmlFor="textinput"> { this.props.description } </label>
                         </div>
                         <div>
-                            <input
-                                id="textinput"
-                                ref={this._textinput}
+                            <Field
+                                id="mx_TextInputDialog_field"
                                 className="mx_TextInputDialog_input"
-                                defaultValue={this.props.value}
-                                autoFocus={this.props.focus}
-                                placeholder={this.props.placeholder}
-                                size="64" />
+                                ref={this._field}
+                                type="text"
+                                label={this.props.placeholder}
+                                value={this.state.value}
+                                onChange={this.onChange}
+                                onValidate={this.props.validator ? this.onValidate : undefined}
+                                size="64"
+                            />
                         </div>
                     </div>
                 </form>
diff --git a/src/components/views/directory/NetworkDropdown.js b/src/components/views/directory/NetworkDropdown.js
index c4a70c112e..6d1501ca57 100644
--- a/src/components/views/directory/NetworkDropdown.js
+++ b/src/components/views/directory/NetworkDropdown.js
@@ -35,6 +35,7 @@ import {useSettingValue} from "../../../hooks/useSettings";
 import * as sdk from "../../../index";
 import Modal from "../../../Modal";
 import SettingsStore from "../../../settings/SettingsStore";
+import withValidation from "../elements/Validation";
 
 export const ALL_ROOMS = Symbol("ALL_ROOMS");
 
@@ -47,6 +48,34 @@ const inPlaceOf = (elementRect) => ({
     chevronFace: "none",
 });
 
+const validServer = withValidation({
+    rules: [
+        {
+            key: "required",
+            test: async ({ value }) => !!value,
+            invalid: () => _t("Enter a server address"),
+        }, {
+            key: "available",
+            final: true,
+            test: async ({ value }) => {
+                try {
+                    const opts = {
+                        limit: 1,
+                        server: value,
+                    };
+                    // check if we can successfully load this server's room directory
+                    await MatrixClientPeg.get().publicRooms(opts);
+                    return true;
+                } catch (e) {
+                    return false;
+                }
+            },
+            valid: () => _t("Looks good"),
+            invalid: () => _t("Can't find this server or its room list"),
+        },
+    ],
+});
+
 // This dropdown sources homeservers from three places:
 // + your currently connected homeserver
 // + homeservers in config.json["roomDirectory"]
@@ -188,6 +217,7 @@ const NetworkDropdown = ({onOptionChange, protocols = {}, selectedServerName, se
                 button: _t("Add"),
                 hasCancel: false,
                 placeholder: _t("Server address"),
+                validator: validServer,
             });
 
             const [ok, newServer] = await finished;
diff --git a/src/i18n/strings/en_EN.json b/src/i18n/strings/en_EN.json
index 59bc643539..3f20d4ec61 100644
--- a/src/i18n/strings/en_EN.json
+++ b/src/i18n/strings/en_EN.json
@@ -1437,6 +1437,9 @@
     "And %(count)s more...|other": "And %(count)s more...",
     "ex. @bob:example.com": "ex. @bob:example.com",
     "Add User": "Add User",
+    "Enter a server address": "Enter a server address",
+    "Looks good": "Looks good",
+    "Can't find this server or its room list": "Can't find this server or its room list",
     "All rooms": "All rooms",
     "Your server": "Your server",
     "Are you sure you want to remove <b>%(serverName)s</b>": "Are you sure you want to remove <b>%(serverName)s</b>",