diff --git a/src/integrators/type.jl b/src/integrators/type.jl
index 7536ac0..42ff7fa 100644
--- a/src/integrators/type.jl
+++ b/src/integrators/type.jl
@@ -28,73 +28,216 @@ function (integrator::HistoryODEIntegrator)(val::AbstractArray,
     OrdinaryDiffEq.current_interpolant!(val, t, integrator, idxs, deriv)
 end
 
-mutable struct DDEIntegrator{algType, IIP, uType, tType, P, eigenType, tTypeNoUnits,
-    tdirType,
-    ksEltype, SolType, F, CacheType, IType, FP, O, dAbsType,
-    dRelType, H,
-    tstopsType, discType, FSALType, EventErrorType,
-    CallbackCacheType, DV} <:
-               AbstractDDEIntegrator{algType, IIP, uType, tType}
-    sol::SolType
-    u::uType
-    k::ksEltype
-    t::tType
-    dt::tType
-    f::F
-    p::P
-    uprev::uType
-    uprev2::uType
-    tprev::tType
-    prev_idx::Int
-    prev2_idx::Int
-    fpsolver::FP
-    order_discontinuity_t0::Int
-    "Discontinuities tracked by callback."
-    tracked_discontinuities::Vector{Discontinuity{tType, Int}}
-    discontinuity_interp_points::Int
-    discontinuity_abstol::dAbsType
-    discontinuity_reltol::dRelType
-    "Future time stops for propagated discontinuities."
-    tstops_propagated::tstopsType
-    "Future propagated discontinuities."
-    d_discontinuities_propagated::discType
-    alg::algType
-    dtcache::tType
-    dtchangeable::Bool
-    dtpropose::tType
-    tdir::tdirType
-    eigen_est::eigenType
-    EEst::tTypeNoUnits
-    qold::tTypeNoUnits
-    q11::tTypeNoUnits
-    erracc::tTypeNoUnits
-    dtacc::tType
-    success_iter::Int
-    iter::Int
-    saveiter::Int
-    saveiter_dense::Int
-    cache::CacheType
-    callback_cache::CallbackCacheType
-    kshortsize::Int
-    force_stepfail::Bool
-    last_stepfail::Bool
-    just_hit_tstop::Bool
-    do_error_check::Bool
-    event_last_time::Int
-    vector_event_last_time::Int
-    last_event_error::EventErrorType
-    accept_step::Bool
-    isout::Bool
-    reeval_fsal::Bool
-    u_modified::Bool
-    isdae::Bool
-    opts::O
-    stats::SciMLBase.DEStats
-    history::H
-    differential_vars::DV
-    integrator::IType
-    fsalfirst::FSALType
-    fsallast::FSALType
+@static if isdefined(OrdinaryDiffEq, :get_fsalfirstlast)
+    mutable struct DDEIntegrator{algType, IIP, uType, tType, P, eigenType, tTypeNoUnits,
+        tdirType,
+        ksEltype, SolType, F, CacheType, IType, FP, O, dAbsType,
+        dRelType, H,
+        tstopsType, discType, FSALType, EventErrorType,
+        CallbackCacheType, DV} <:
+                   AbstractDDEIntegrator{algType, IIP, uType, tType}
+        sol::SolType
+        u::uType
+        k::ksEltype
+        t::tType
+        dt::tType
+        f::F
+        p::P
+        uprev::uType
+        uprev2::uType
+        tprev::tType
+        prev_idx::Int
+        prev2_idx::Int
+        fpsolver::FP
+        order_discontinuity_t0::Int
+        "Discontinuities tracked by callback."
+        tracked_discontinuities::Vector{Discontinuity{tType, Int}}
+        discontinuity_interp_points::Int
+        discontinuity_abstol::dAbsType
+        discontinuity_reltol::dRelType
+        "Future time stops for propagated discontinuities."
+        tstops_propagated::tstopsType
+        "Future propagated discontinuities."
+        d_discontinuities_propagated::discType
+        alg::algType
+        dtcache::tType
+        dtchangeable::Bool
+        dtpropose::tType
+        tdir::tdirType
+        eigen_est::eigenType
+        EEst::tTypeNoUnits
+        qold::tTypeNoUnits
+        q11::tTypeNoUnits
+        erracc::tTypeNoUnits
+        dtacc::tType
+        success_iter::Int
+        iter::Int
+        saveiter::Int
+        saveiter_dense::Int
+        cache::CacheType
+        callback_cache::CallbackCacheType
+        kshortsize::Int
+        force_stepfail::Bool
+        last_stepfail::Bool
+        just_hit_tstop::Bool
+        do_error_check::Bool
+        event_last_time::Int
+        vector_event_last_time::Int
+        last_event_error::EventErrorType
+        accept_step::Bool
+        isout::Bool
+        reeval_fsal::Bool
+        u_modified::Bool
+        isdae::Bool
+        opts::O
+        stats::SciMLBase.DEStats
+        history::H
+        differential_vars::DV
+        integrator::IType
+        fsalfirst::FSALType
+        fsallast::FSALType
+    end
+    
+else
+    mutable struct DDEIntegrator{algType, IIP, uType, tType, P, eigenType, tTypeNoUnits,
+        tdirType,
+        ksEltype, SolType, F, CacheType, IType, FP, O, dAbsType,
+        dRelType, H,
+        tstopsType, discType, FSALType, EventErrorType,
+        CallbackCacheType, DV} <:
+                AbstractDDEIntegrator{algType, IIP, uType, tType}
+        sol::SolType
+        u::uType
+        k::ksEltype
+        t::tType
+        dt::tType
+        f::F
+        p::P
+        uprev::uType
+        uprev2::uType
+        tprev::tType
+        prev_idx::Int
+        prev2_idx::Int
+        fpsolver::FP
+        order_discontinuity_t0::Int
+        "Discontinuities tracked by callback."
+        tracked_discontinuities::Vector{Discontinuity{tType, Int}}
+        discontinuity_interp_points::Int
+        discontinuity_abstol::dAbsType
+        discontinuity_reltol::dRelType
+        "Future time stops for propagated discontinuities."
+        tstops_propagated::tstopsType
+        "Future propagated discontinuities."
+        d_discontinuities_propagated::discType
+        alg::algType
+        dtcache::tType
+        dtchangeable::Bool
+        dtpropose::tType
+        tdir::tdirType
+        eigen_est::eigenType
+        EEst::tTypeNoUnits
+        qold::tTypeNoUnits
+        q11::tTypeNoUnits
+        erracc::tTypeNoUnits
+        dtacc::tType
+        success_iter::Int
+        iter::Int
+        saveiter::Int
+        saveiter_dense::Int
+        cache::CacheType
+        callback_cache::CallbackCacheType
+        kshortsize::Int
+        force_stepfail::Bool
+        last_stepfail::Bool
+        just_hit_tstop::Bool
+        do_error_check::Bool
+        event_last_time::Int
+        vector_event_last_time::Int
+        last_event_error::EventErrorType
+        accept_step::Bool
+        isout::Bool
+        reeval_fsal::Bool
+        u_modified::Bool
+        isdae::Bool
+        opts::O
+        stats::SciMLBase.DEStats
+        history::H
+        differential_vars::DV
+        integrator::IType
+        fsalfirst::FSALType
+        fsallast::FSALType
+
+        # incomplete initialization without fsalfirst and fsallast
+        function DDEIntegrator{algType, IIP, uType, tType, P, eigenType, tTypeNoUnits,
+                tdirType, ksEltype, SolType, F, CacheType, IType, FP,
+                O, dAbsType, dRelType, H, tstopsType, discType,
+                FSALType, EventErrorType, CallbackCacheType, DV}(sol, u, k, t, dt, f,
+                p, uprev, uprev2,
+                tprev, prev_idx,
+                prev2_idx,
+                fpsolver,
+                order_discontinuity_t0,
+                tracked_discontinuities,
+                discontinuity_interp_points,
+                discontinuity_abstol,
+                discontinuity_reltol,
+                tstops_propagated,
+                d_discontinuities_propagated,
+                alg, dtcache,
+                dtchangeable,
+                dtpropose, tdir,
+                eigen_est, EEst,
+                qold,
+                q11, erracc, dtacc,
+                success_iter, iter,
+                saveiter,
+                saveiter_dense,
+                cache,
+                callback_cache,
+                kshortsize,
+                force_stepfail,
+                last_stepfail,
+                just_hit_tstop,
+                do_error_check,
+                event_last_time,
+                vector_event_last_time,
+                last_event_error,
+                accept_step, isout,
+                reeval_fsal,
+                u_modified, isdae,
+                opts, stats,
+                history,
+                differential_vars,
+                integrator) where
+                {algType, IIP, uType, tType, P, eigenType, tTypeNoUnits, tdirType, ksEltype,
+                SolType, F,
+                CacheType, IType, FP, O, dAbsType, dRelType, H, tstopsType, discType,
+                FSALType, EventErrorType, CallbackCacheType, DV}
+            new{algType, IIP, uType, tType, P, eigenType, tTypeNoUnits, tdirType, ksEltype,
+                SolType, F,
+                CacheType, IType, FP, O, dAbsType, dRelType, H, tstopsType, discType, FSALType,
+                EventErrorType, CallbackCacheType, DV}(
+                sol, u, k, t, dt, f, p, uprev, uprev2, tprev,
+                prev_idx, prev2_idx, fpsolver,
+                order_discontinuity_t0,
+                tracked_discontinuities,
+                discontinuity_interp_points,
+                discontinuity_abstol, discontinuity_reltol,
+                tstops_propagated,
+                d_discontinuities_propagated, alg, dtcache,
+                dtchangeable, dtpropose, tdir,
+                eigen_est, EEst, qold, q11, erracc, dtacc,
+                success_iter, iter, saveiter, saveiter_dense,
+                cache, callback_cache, kshortsize,
+                force_stepfail, last_stepfail,
+                just_hit_tstop,
+                do_error_check, event_last_time,
+                vector_event_last_time,
+                last_event_error, accept_step, isout,
+                reeval_fsal, u_modified, isdae, opts,
+                stats, history, differential_vars, integrator)
+        end
+    end
 end
 
 function (integrator::DDEIntegrator)(t, deriv::Type = Val{0}; idxs = nothing)