diff --git a/src/core/dynamicalsystem_interface.jl b/src/core/dynamicalsystem_interface.jl
index cacb859b..3cb1ca97 100644
--- a/src/core/dynamicalsystem_interface.jl
+++ b/src/core/dynamicalsystem_interface.jl
@@ -185,12 +185,8 @@ state of the system is the full state space state, not the projected one
 (this makes the most sense for allowing MTK-based indexing).
 This function does not work with [`PoincareMap`](@ref) and [`ParallelDynamicalSystem`](@ref).
 """
-function observe_state(ds::DynamicalSystem, index)
-    u = current_state(ds)
+function observe_state(ds::DynamicalSystem, index, u = current_state(ds))
     prob, sys, integ = referrenced_sciml_sys(ds)
-    observe_state(u, prob, sys, integ, index)
-end
-function observe_state(u, prob, sys, integ, index)
     if !has_referrenced_sys(sys)
         T = eltype(u)
         if index isa Int
@@ -200,7 +196,7 @@ function observe_state(u, prob, sys, integ, index)
         end
     else
         ugetter = SymbolicIndexingInterface.getu(sys, index)
-        return ugetter(integ)
+        return ugetter(u)
     end
 end
 
@@ -226,19 +222,17 @@ current_parameters(ds::DynamicalSystem) = ds.p
 Return the specific parameter corresponding to `index`,
 which can be anything given to [`set_parameter!`](@ref).
 """
-current_parameter(ds::DynamicalSystem, index) = current_paramter(ds, current_parameters(ds), index)
-function current_parameter(ds::DynamicalSystem, p, index)
+function current_parameter(ds::DynamicalSystem, index, p = current_parameters(ds))
     prob, sys, integ = referrenced_sciml_sys(ds)
     if !has_referrenced_sys(sys)
         return _get_parameter(p, index)
-    else # symbolic dispatch # TODO: Use the `observed` function directly on `p`.
+    else # symbolic dispatch
         i = SymbolicIndexingInterface.getp(sys, index)
-        return i(prob)
+        return i(p)
     end
 end
-
-# Dispatch for composite types as parameter containers
 _get_parameter(p::Union{AbstractArray, AbstractDict}, index) = getindex(p, index)
+# Dispatch for composite types as parameter containers
 _get_parameter(p, index) = getproperty(p, index)
 
 """
@@ -248,10 +242,6 @@ Return the initial parameter container of `ds`.
 This is never mutated and is set when initializing `ds`.
 """
 initial_parameters(ds::DynamicalSystem) = ds.p0
-function initial_parameters(ds::DynamicalSystem, index)
-    i = parameter_index(ds, index)
-    return _get_parameter(initial_parameters(ds), i)
-end
 
 """
     isdeterministic(ds::DynamicalSystem) → true/false
@@ -336,23 +326,25 @@ and the `value` to set it to. This function works for any type of parameter cont
 (array/dictionary/composite types) provided the `index` is appropriate type.
 
 The `index` can be a traditional Julia index (integer for arrays, key for dictionaries,
-or symbol for composite types). However, it can also be a symbolic variable.
+or symbol for composite types). It can also be a symbolic variable.
 This is valid only for dynamical systems referring a ModelingToolkit.jl model
 which also has `index` as one of its parameters.
 """
-set_parameter!(ds::DynamicalSystem, args...) = _set_parameter!(ds, current_parameters(ds), args...)
-
-function _set_parameter!(ds::DynamicalSystem, p, index, value)
+function set_parameter!(ds::DynamicalSystem, index, value, p = current_parameters(ds))
+    # internal function is necessary so that we are able to call `u_modified!` for ODEs.
+    _set_parameter!(ds::DynamicalSystem, index, value, p)
+end
+function _set_parameter!(ds::DynamicalSystem, index, value, p = current_parameters(ds))
     prob, sys = referrenced_sciml_sys(ds)
-    if !has_referrenced_sys(prob)
+    if !has_referrenced_sys(sys)
         if p isa Union{AbstractArray, AbstractDict}
             setindex!(p, value, index)
         else
             setproperty!(p, index, value)
         end
     else
-        i = SymbolicIndexingInterface.setp(sys, index)
-        i(prob, value)
+        set! = SymbolicIndexingInterface.setp(sys, index)
+        set!(p, value)
     end
     return
 end
diff --git a/src/core_systems/continuous_time_ode.jl b/src/core_systems/continuous_time_ode.jl
index 333e70f4..7c6270a5 100644
--- a/src/core_systems/continuous_time_ode.jl
+++ b/src/core_systems/continuous_time_ode.jl
@@ -168,7 +168,7 @@ end
 
 # This is here to ensure that `u_modified!` is called
 function set_parameter!(ds::CoupledODEs, args...)
-    _set_parameter!(ds, current_parameters(ds), args...)
+    _set_parameter!(ds, args...)
     u_modified!(ds.integ, true)
     return
 end
diff --git a/test/mtk_integration.jl b/test/mtk_integration.jl
index 1e836eda..90f7ff74 100644
--- a/test/mtk_integration.jl
+++ b/test/mtk_integration.jl
@@ -27,10 +27,6 @@ connected = compose(ODESystem(connections, name = :connected), fol_1, fol_2)
 
 connected_simp = structural_simplify(connected)
 
-using DynamicalSystemsBase.SymbolicIndexingInterface
-# SymbolicIndexingInterface.observed(connected_simp, fol_1.τ)
-# SymbolicIndexingInterface.state_values(arr::AbstractArray) = arr
-
 u0 = [fol_1.x => -0.5,
     fol_2.x => 1.0]