No bean resolver registered in the context to resolve access to bean

I'm trying to implement method security using Java Config, but I'm getting a error:-

org.springframework.expression.spel.SpelEvaluationException: EL1057E:(pos 1): No bean resolver registered in the context to resolve access to bean 'appPermissionEvaluator'

The method is:-

@PreAuthorize("@appPermissionEvaluator.hasSystemPermission()")
public String something() {
    ...
}

The Config class definition is (MethodSecurityConfig.java):-

@Configuration
@EnableGlobalMethodSecurity(prePostEnabled = true)
public class MethodSecurityConfig extends GlobalMethodSecurityConfiguration {

    @Bean
    public AppPermissionEvaluator appPermissionEvaluator() {
        return new AppPermissionEvaluator();
    }

    @Override
    protected MethodSecurityExpressionHandler createExpressionHandler() {
        DefaultMethodSecurityExpressionHandler expressionHandler =
                new DefaultMethodSecurityExpressionHandler();
        expressionHandler.setPermissionEvaluator(appPermissionEvaluator());
        return expressionHandler;
    }

    ...
}

I'm not sure what's going wrong. Any Pointers?