Chi-squared approximation may be incorrect in: chisq.test(x)

I am getting "Chi-squared approximation may be incorrect in:
chisq.test(x)"  with the data bleow.

Frequency distribution of number of male offspring in families of size 5.
Number of Male Offspring 	N
0 		                          518
1 		                         2245
2 		                          4621
3 		                          4753
4 		                          2476
5 		                            549
Total 		                      15,162

x=matrix(c(0,1,2,3,4,5,518,2245,4621,4753,2476,549), ncol=2)
x

[,1] [,2]
[1,]    0  518
[2,]    1 2245
[3,]    2 4621
[4,]    3 4753
[5,]    4 2476
[6,]    5  549

chisq.test(x)

Pearson's Chi-squared test

data:  x
X-squared = 40.4672, df = 5, p-value = 1.202e-07

Warning message:
Chi-squared approximation may be incorrect in: chisq.test(x)

Does the warning mean that chisq.test(x) can't be used for this data.

If chisq.test(x) can't be used for this data, which test is to be used?

Pls advise.

thx

ej