diff --git a/src/nlsolve/muller.jl b/src/nlsolve/muller.jl
index d1bf039..b05b5f4 100644
--- a/src/nlsolve/muller.jl
+++ b/src/nlsolve/muller.jl
@@ -13,6 +13,7 @@ function SciMLBase.solve(prob::NonlinearProblem, alg::SimpleMuller, args...;
     @assert !isinplace(prob) "`SimpleMuller` only supports OOP problems."
     @assert length(prob.u0) == 3 "`SimpleMuller` requires three initial guesses."
     xᵢ₋₂, xᵢ₋₁, xᵢ = prob.u0
+    xᵢ₋₂, xᵢ₋₁, xᵢ = promote(xᵢ₋₂, xᵢ₋₁, xᵢ)
     @assert xᵢ₋₂ ≠ xᵢ₋₁ ≠ xᵢ ≠ xᵢ₋₂
     f = Base.Fix2(prob.f, prob.p)
     fxᵢ₋₂, fxᵢ₋₁, fxᵢ = f(xᵢ₋₂), f(xᵢ₋₁), f(xᵢ)
@@ -20,6 +21,8 @@ function SciMLBase.solve(prob::NonlinearProblem, alg::SimpleMuller, args...;
     abstol = __get_tolerance(nothing, abstol,
             promote_type(eltype(fxᵢ₋₂), eltype(xᵢ₋₂)))
 
+    xᵢ₊₁, fxᵢ₊₁ = xᵢ₋₂, fxᵢ₋₂
+
     for _ ∈ 1:maxiters
         q = (xᵢ - xᵢ₋₁)/(xᵢ₋₁ - xᵢ₋₂)
         A = q*fxᵢ - q*(1 + q)*fxᵢ₋₁ + q^2*fxᵢ₋₂