diff --git a/src/core/__tests__/theming.test.tsx b/src/core/__tests__/theming.test.tsx
index cb61aef20d..3ae5d44691 100644
--- a/src/core/__tests__/theming.test.tsx
+++ b/src/core/__tests__/theming.test.tsx
@@ -264,6 +264,26 @@ describe('adaptNavigationTheme', () => {
     });
   });
 
+  it('should keep fonts and custom colors when adapting a single theme', () => {
+    const { LightTheme: navLight } = adaptNavigationTheme({
+      reactNavigationLight: {
+        ...NavigationThemeWithFonts,
+        colors: NavigationCustomLightTheme.colors,
+      },
+    });
+    const { DarkTheme: navDark } = adaptNavigationTheme({
+      reactNavigationDark: { ...NavigationThemeWithFonts, dark: true },
+    });
+
+    expect(navLight.colors.secondary).toBe('rgb(150,45,85)');
+    expect(navLight.fonts.regular.fontFamily).toBe(
+      LightTheme.fonts.bodyMedium.fontFamily
+    );
+    expect(navDark.fonts.regular.fontFamily).toBe(
+      DarkTheme.fonts.bodyMedium.fontFamily
+    );
+  });
+
   it('should not expect fonts on theme without fonts', () => {
     const { LightTheme: navLight, DarkTheme: navDark } = adaptNavigationTheme({
       reactNavigationLight: NavigationLightTheme,
diff --git a/src/theme/provider.tsx b/src/theme/provider.tsx
index 8f7e77681e..2c1f8ca9f9 100644
--- a/src/theme/provider.tsx
+++ b/src/theme/provider.tsx
@@ -75,14 +75,14 @@ export function adaptNavigationTheme<T extends NavigationTheme>(themes: {
   reactNavigationLight: T;
   materialLight?: Theme;
 }): {
-  LightTheme: NavigationTheme;
+  LightTheme: T;
 };
 // eslint-disable-next-line no-redeclare
 export function adaptNavigationTheme<T extends NavigationTheme>(themes: {
   reactNavigationDark: T;
   materialDark?: Theme;
 }): {
-  DarkTheme: NavigationTheme;
+  DarkTheme: T;
 };
 // eslint-disable-next-line no-redeclare
 export function adaptNavigationTheme<