diff --git a/math.jl b/math.jl
index 4a3fec5..0556def 100644
--- a/math.jl
+++ b/math.jl
@@ -15,7 +15,7 @@ laguerre(l, n, x) = gamma(n + l + 3/2) * better_sum([(-x * x)^k / gamma(k + l +
 ho_basis(l, n, x) = (-1)^n / sqrt_sqrt_pi * 2^((n + l + 2) / 2) * sqrt_factorial(n) / sqrt_double_factorial(2*n + 2*l + 1) * x^(l + 1) * exp(-x^2 / 2) * laguerre(l, n, x)
 
 # for implementation of simple relative coordinates
-double_factorial(n) = Iterators.prod(n:-2:1)
+double_factorial(n) = Iterators.prod(Float64, n:-2:1)
 
 "Gaussian integral for n ∈ Integers (Ref: Wolfram MathWorld + simplifications)"
 gauss_int(a, n) = double_factorial(n - 1) / (2 * a)^((n + 1)/2) * (iseven(n) ? sqrt(π / 2) : 1)