Reliable standard errors for mixed effects models in the lme4 R package

I am using the lme4 package to simulate a linear blended effect

the mixed effect model is below:

fm01 <- lmer(sublat <- goal + (1|userid))

      

        
        
        
      

    

the above command returns an S4 object named fm01

this object includes fixed effects and their OLS standard errors (below)

Fixed effects:

            Estimate Std. Error t value
(Intercept)   31.644      3.320   9.530
goaltypeF1    -4.075      3.243  -1.257
goaltypeF2    -9.187      5.609  -1.638
goaltypeF3   -13.935      9.455  -1.474
goaltypeF4   -20.219      8.196  -2.467
goaltypeF5   -12.134      8.797  -1.379"

      

        
        
        
      

    

however i need to provide robust standard errors

Does anyone know the code or package to do this with an S4 object like returned by lme4?

Thank!

Adrienne