diff --git a/public/locales/en.json b/public/locales/en.json
index 7b23443..b8d485e 100644
--- a/public/locales/en.json
+++ b/public/locales/en.json
@@ -408,6 +408,7 @@
     "autoRefreshNamePage": "Auto-refresh name page",
 
     "subMenuAdvanced": "Advanced settings",
+    "modalAuth": "Always prompt for master password with a modal dialog",
     "alwaysIncludeMined": "Always include mined transactions in transaction listings (may require refresh)",
     "copyNameSuffixes": "Include suffix when copying names",
     "addressCopyButtons": "Show copy buttons next to all addresses",
diff --git a/src/components/auth/AuthMasterPasswordModal.tsx b/src/components/auth/AuthMasterPasswordModal.tsx
new file mode 100644
index 0000000..52470eb
--- /dev/null
+++ b/src/components/auth/AuthMasterPasswordModal.tsx
@@ -0,0 +1,42 @@
+// Copyright (c) 2020-2021 Drew Lemmy
+// This file is part of KristWeb 2 under AGPL-3.0.
+// Full details: https://github.com/tmpim/KristWeb2/blob/master/LICENSE.txt
+import { useRef } from "react";
+import { Modal, Input } from "antd";
+
+import { useTFns } from "@utils/i18n";
+
+import { useAuthForm } from "./AuthMasterPasswordPopover";
+
+interface Props {
+  visible: boolean;
+  encrypt?: boolean;
+  onCancel: () => void;
+  onSubmit: () => void;
+}
+
+export function AuthMasterPasswordModal({
+  visible,
+  encrypt,
+  onCancel,
+  onSubmit
+}: Props): JSX.Element {
+  const { t, tStr } = useTFns("masterPassword.");
+  const inputRef = useRef<Input>(null);
+
+  const { form, submit, reset } = useAuthForm({ encrypt, onSubmit, inputRef });
+
+  return <Modal
+    title={tStr("dialogTitle")}
+    okText={tStr("popoverAuthoriseButton")}
+    cancelText={t("dialog.cancel")}
+
+    visible={visible}
+    destroyOnClose
+
+    onCancel={() => { reset(); onCancel(); }}
+    onOk={submit}
+  >
+    {form}
+  </Modal>;
+}
diff --git a/src/components/auth/AuthMasterPasswordPopover.tsx b/src/components/auth/AuthMasterPasswordPopover.tsx
index 26c0054..5b7952d 100644
--- a/src/components/auth/AuthMasterPasswordPopover.tsx
+++ b/src/components/auth/AuthMasterPasswordPopover.tsx
@@ -1,7 +1,7 @@
 // Copyright (c) 2020-2021 Drew Lemmy
 // This file is part of KristWeb 2 under AGPL-3.0.
 // Full details: https://github.com/tmpim/KristWeb2/blob/master/LICENSE.txt
-import { useState, useRef, useCallback, FC, Ref } from "react";
+import { useState, useRef, useMemo, useCallback, FC, Ref } from "react";
 import { Popover, Button, Input, Form } from "antd";
 import { TooltipPlacement } from "antd/lib/tooltip";
 
@@ -62,23 +62,54 @@
   onSubmit,
   inputRef
 }: AuthFormProps): JSX.Element {
+  const { tStr } = useTFns("masterPassword.");
+
+  const { form, submit } = useAuthForm({ encrypt, onSubmit, inputRef });
+
+  return <>
+    {form}
+
+    {/* Submit button */}
+    <Button type="primary" size="small" onClick={submit}>
+      {tStr("popoverAuthoriseButton")}
+    </Button>
+  </>;
+}
+
+interface AuthFormRes {
+  form: JSX.Element;
+  submit: () => Promise<void>;
+  reset: () => void;
+}
+
+export function useAuthForm({
+  encrypt,
+  onSubmit,
+  inputRef
+}: AuthFormProps): AuthFormRes {
   const { t, tStr, tKey } = useTFns("masterPassword.");
 
   const { salt, tester } = useMasterPassword();
 
-  const [form] = Form.useForm();
+  const [form] = Form.useForm<FormValues>();
   const [passwordError, setPasswordError] = useState<string | undefined>();
 
-  const onFinish = useCallback(async function(values: FormValues) {
+  const reset = useCallback(() => {
+    form.resetFields();
+  }, [form]);
+
+  const onFinish = useCallback(async function() {
+    const values = await form.validateFields();
+
     try {
       await authMasterPassword(salt, tester, values.masterPassword);
       onSubmit();
     } catch (err) {
       setPasswordError(translateError(t, err, tKey("errorUnknown")));
     }
-  }, [t, tKey, onSubmit, salt, tester]);
+  }, [t, tKey, onSubmit, salt, tester, form]);
 
-  return <>
+  const formEl = useMemo(() => <>
     <p>{tStr(encrypt ? "popoverDescriptionEncrypt" : "popoverDescription")}</p>
 
     <Form
@@ -98,23 +129,23 @@
         help={passwordError}
 
         rules={[
-          { required: true, message: t("masterPassword.errorPasswordRequired") },
-          { min: 0, message: t("masterPassword.errorPasswordLength") },
+          { required: true, message: tStr("errorPasswordRequired") },
+          { min: 0, message: tStr("errorPasswordLength") },
         ]}
 
         style={{ marginBottom: 8 }}
       >
         {getMasterPasswordInput({
           inputRef,
-          placeholder: t("masterPassword.passwordPlaceholder"),
+          placeholder: tStr("passwordPlaceholder"),
           autoFocus: true
         })}
       </Form.Item>
 
-      {/* Submit button */}
-      <Button type="primary" htmlType="submit" size="small">
-        {t("masterPassword.popoverAuthoriseButton")}
-      </Button>
+      {/* Fake submit button to allow the enter key to submit in modal */}
+      <Button htmlType="submit" style={{ display: "none" }} />
     </Form>
-  </>;
+  </>, [tStr, inputRef, encrypt, form, onFinish, passwordError]);
+
+  return { form: formEl, submit: onFinish, reset };
 }
diff --git a/src/components/auth/AuthorisedAction.tsx b/src/components/auth/AuthorisedAction.tsx
index ac21f39..223656a 100644
--- a/src/components/auth/AuthorisedAction.tsx
+++ b/src/components/auth/AuthorisedAction.tsx
@@ -2,11 +2,14 @@
 // This file is part of KristWeb 2 under AGPL-3.0.
 // Full details: https://github.com/tmpim/KristWeb2/blob/master/LICENSE.txt
 import React, { FC, useState } from "react";
+import { Grid } from "antd";
 import { TooltipPlacement } from "antd/lib/tooltip";
 
 import { useMasterPassword } from "@wallets";
+import { useBooleanSetting } from "@utils/settings";
 
 import { AuthMasterPasswordPopover } from "./AuthMasterPasswordPopover";
+import { AuthMasterPasswordModal } from "./AuthMasterPasswordModal";
 import { SetMasterPasswordModal } from "./SetMasterPasswordModal";
 
 import "./AuthorisedAction.less";
@@ -27,6 +30,11 @@
   // Don't render the modal and popover unless we absolutely have to
   const [clicked, setClicked] = useState(false);
   const [modalVisible, setModalVisible] = useState(false);
+  const [authModalVisible, setAuthModalVisible] = useState(false);
+
+  // Determine whether to use a popover or a modal for auth
+  const bps = Grid.useBreakpoint();
+  const alwaysModal = useBooleanSetting("modalAuth");
 
   // This is used to pass the 'onClick' prop down to the child. The child MUST
   // support the onClick prop.
@@ -41,8 +49,7 @@
     return React.cloneElement(child, { onClick: (e: MouseEvent) => {
       e.preventDefault();
       debug("authorised action occurred: was already authed");
-
-      if (onAuthed) onAuthed();
+      onAuthed?.();
     }});
   } else if (!hasMasterPassword) {
     // The user does not yet have a master password, prompt them to create one:
@@ -51,7 +58,7 @@
         e.preventDefault();
         debug("authorised action postponed: no master password set");
 
-        if (!clicked) setClicked(true);
+        setClicked(true);
         setModalVisible(true);
       }})}
 
@@ -62,18 +69,40 @@
           debug("authorised action occurred: master password now set, continuing with action");
 
           setModalVisible(false);
-          if (onAuthed) onAuthed();
+          onAuthed?.();
+        }}
+      />}
+    </>;
+  } else if (!bps.md || alwaysModal) {
+    // The user has a master password set but is not logged in, prompt them to
+    // enter it. Show a modal on mobile:
+    return <>
+      {React.cloneElement(child, { onClick: (e: MouseEvent) => {
+        e.preventDefault();
+        debug("authorised action postponed: no master password set");
+
+        setClicked(true);
+        setAuthModalVisible(true);
+      }})}
+
+      {clicked && <AuthMasterPasswordModal
+        visible={authModalVisible}
+        onCancel={() => setAuthModalVisible(false)}
+        onSubmit={() => {
+          debug("authorised action occurred: master password now set, continuing with action");
+
+          setAuthModalVisible(false);
+          onAuthed?.();
         }}
       />}
     </>;
   } else {
-    // The user has a master password set but is not logged in, prompt them to
-    // enter it:
+    // Show a popover on desktop:
     return <AuthMasterPasswordPopover
       encrypt={encrypt}
       onSubmit={() => {
         debug("authorised action occurred: master password provided");
-        if (onAuthed) onAuthed();
+        onAuthed?.();
       }}
       placement={popoverPlacement}
     >
diff --git a/src/pages/settings/SettingsPage.tsx b/src/pages/settings/SettingsPage.tsx
index cc55b68..eaa6732 100644
--- a/src/pages/settings/SettingsPage.tsx
+++ b/src/pages/settings/SettingsPage.tsx
@@ -56,6 +56,7 @@
         subKey="Advanced"
         icon={<SettingOutlined />}
         settings={[
+          booleanSetting("modalAuth"),
           booleanSetting("alwaysIncludeMined"),
           booleanSetting("copyNameSuffixes"),
           booleanSetting("addressCopyButtons"),
diff --git a/src/utils/settings.ts b/src/utils/settings.ts
index 7dd362a..3717a5c 100644
--- a/src/utils/settings.ts
+++ b/src/utils/settings.ts
@@ -32,6 +32,8 @@
   // ===========================================================================
   // ADVANCED SETTINGS
   // ===========================================================================
+  /** Always prompt for master password with a modal dialog. */
+  readonly modalAuth: boolean;
   /** Always include mined transactions by default in transaction listings. */
   readonly alwaysIncludeMined: boolean;
   /** Whether or not to include the name suffix when copying a name. */
@@ -77,6 +79,7 @@
   autoRefreshAddressPage: true,
   autoRefreshNamePage: true,
 
+  modalAuth: true,
   alwaysIncludeMined: false,
   copyNameSuffixes: true,
   addressCopyButtons: false,