### Function defined with an integral

Dear all,
I'm puzzled by this answer from Sage:

sage: def f(x):
....: return integral(exp(t^2)/sqrt(t),t,1,x^2)
sage: f(4).numerical_approx()
1.18428615262607e109 - 1.28184667602042*I

Why the answer is a complex number? How can I define f as a real function?
Thanks.