diff --git a/src/platform/web/ThemeLoader.ts b/src/platform/web/ThemeLoader.ts
index 94310b80..e278b9a6 100644
--- a/src/platform/web/ThemeLoader.ts
+++ b/src/platform/web/ThemeLoader.ts
@@ -165,9 +165,9 @@ export class ThemeLoader {
     getDefaultTheme(): string | undefined {
         switch (this.preferredColorScheme) {
             case ColorSchemePreference.Dark:
-                return this._platform.config["defaultTheme"].dark;
+                return this._platform.config["defaultTheme"]?.dark;
             case ColorSchemePreference.Light:
-                return this._platform.config["defaultTheme"].light;
+                return this._platform.config["defaultTheme"]?.light;
         }
     }