diff --git a/mobile/lib/app.dart b/mobile/lib/app.dart
index 7a2e62ce9f..4a3cd4320e 100644
--- a/mobile/lib/app.dart
+++ b/mobile/lib/app.dart
@@ -354,6 +354,19 @@ class App extends HookConsumerWidget {
         ? ref.watch(communityThemeProvider)
         : defaultCommunityTheme;
     final themeMode = communityTheme.mode;
+    // The app rebuilds on every lifecycle change. A new ThemeData never
+    // equals the last one, so MaterialApp would animate between identical
+    // themes, and each frame of that makes every message re-parse its
+    // markdown. Build the themes only when the accent changes.
+    final accent = communityTheme.accent;
+    final lightTheme = useMemoized(
+      () => mobileAppearanceTheme(Brightness.light, accent),
+      [accent],
+    );
+    final darkTheme = useMemoized(
+      () => mobileAppearanceTheme(Brightness.dark, accent),
+      [accent],
+    );
     final authState = ref.watch(authProvider);
     final pairedCommunity = ref.watch(pairedCommunityLandingProvider);
 
@@ -413,8 +426,8 @@ class App extends HookConsumerWidget {
       navigatorObservers: [appRouteObserver],
       title: 'Buzz',
       debugShowCheckedModeBanner: false,
-      theme: mobileAppearanceTheme(Brightness.light, communityTheme.accent),
-      darkTheme: mobileAppearanceTheme(Brightness.dark, communityTheme.accent),
+      theme: lightTheme,
+      darkTheme: darkTheme,
       themeMode: themeMode,
       // Above the navigator, so an age restriction cannot be bypassed by a
       // route that was pushed while the store signal request was in flight.
diff --git a/mobile/test/shared/theme/app_theme_rebuild_test.dart b/mobile/test/shared/theme/app_theme_rebuild_test.dart
new file mode 100644
index 0000000000..f8e5ffa9ea
--- /dev/null
+++ b/mobile/test/shared/theme/app_theme_rebuild_test.dart
@@ -0,0 +1,72 @@
+import 'package:buzz/app.dart';
+import 'package:buzz/features/age_gate/age_signal_provider.dart';
+import 'package:buzz/shared/auth/auth.dart';
+import 'package:buzz/shared/theme/theme_provider.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:gpt_markdown/gpt_markdown.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+// The app rebuilds on every lifecycle change, so a resume rebuilds it several
+// times. ThemeData has no value equality the app's themes satisfy, so new
+// themes made MaterialApp animate between identical ones, and every frame of
+// that animation made each mounted message re-parse its markdown.
+void main() {
+  testWidgets('an app rebuild keeps its themes and markdown theme', (
+    tester,
+  ) async {
+    SharedPreferences.setMockInitialValues({});
+    final prefs = await SharedPreferences.getInstance();
+    final auth = _SignedOutAuth();
+    final container = ProviderContainer(
+      overrides: [
+        savedPrefsProvider.overrideWithValue(prefs),
+        authProvider.overrideWith(() => auth),
+        ageSignalProvider.overrideWith(_AllowedAgeSignal.new),
+      ],
+    );
+    addTearDown(container.dispose);
+    await tester.pumpWidget(
+      UncontrolledProviderScope(container: container, child: const App()),
+    );
+    await tester.pump(const Duration(seconds: 1));
+
+    MaterialApp app() => tester.widget<MaterialApp>(find.byType(MaterialApp));
+    GptMarkdownThemeData markdown() => tester
+        .widget<GptMarkdownTheme>(find.byType(GptMarkdownTheme).first)
+        .gptThemeData;
+    final theme = app().theme;
+    final darkTheme = app().darkTheme;
+    final markdownTheme = markdown();
+
+    // A new auth state rebuilds the app, as a lifecycle change does.
+    auth.republish();
+    await tester.pump();
+    // Midway through what would be a theme animation.
+    await tester.pump(const Duration(milliseconds: 100));
+
+    expect(identical(app().theme, theme), isTrue);
+    expect(identical(app().darkTheme, darkTheme), isTrue);
+    expect(identical(markdown(), markdownTheme), isTrue);
+
+    await tester.pumpWidget(const SizedBox.shrink());
+  });
+}
+
+class _SignedOutAuth extends AuthNotifier {
+  @override
+  Future<AuthState> build() async =>
+      const AuthState(status: AuthStatus.unauthenticated);
+
+  void republish() =>
+      state = AsyncData(AuthState(status: state.requireValue.status));
+}
+
+class _AllowedAgeSignal extends AgeSignalNotifier {
+  @override
+  AgeSignalState build() => AgeSignalState.allowed;
+
+  @override
+  Future<void> request() async {}
+}