diff --git a/src/parameter_indexing.jl b/src/parameter_indexing.jl
index f64e7d1a..8f4d5ea5 100644
--- a/src/parameter_indexing.jl
+++ b/src/parameter_indexing.jl
@@ -208,11 +208,24 @@ for argType in [Union{Int, CartesianIndex}, Colon, AbstractArray{Bool}, Any]
 end
 
 function (gpo::GetParameterObserved{<:Vector})(::NotTimeseries, prob)
-    gpo.obsfn(parameter_values(prob), current_time(prob))
+    # if the method doesn't exist or is an identity function, then `prob` itself
+    # is the parameter object, so use that and pass `nothing` for the time expecting
+    # it to not be used
+    if hasmethod(parameter_values, Tuple{typeof(prob)}) &&
+       (ps = parameter_values(prob)) != prob
+        gpo.obsfn(ps, current_time(prob))
+    else
+        gpo.obsfn(prob, nothing)
+    end
 end
 function (gpo::GetParameterObserved{<:Vector, true})(
         buffer::AbstractArray, ::NotTimeseries, prob)
-    gpo.obsfn(buffer, parameter_values(prob), current_time(prob))
+    if hasmethod(parameter_values, Tuple{typeof(prob)}) &&
+       (ps = parameter_values(prob)) != prob
+        gpo.obsfn(buffer, ps, current_time(prob))
+    else
+        gpo.obsfn(buffer, prob, nothing)
+    end
 end
 function (gpo::GetParameterObserved{<:Vector})(::Timeseries, prob)
     throw(MixedParameterTimeseriesIndexError(prob, indexer_timeseries_index(gpo)))
@@ -224,10 +237,20 @@ function (gpo::GetParameterObserved{<:Vector, false})(::AbstractArray, ::Timeser
     throw(MixedParameterTimeseriesIndexError(prob, indexer_timeseries_index(gpo)))
 end
 function (gpo::GetParameterObserved)(::NotTimeseries, prob)
-    gpo.obsfn(parameter_values(prob), current_time(prob))
+    if hasmethod(parameter_values, Tuple{typeof(prob)}) &&
+       (ps = parameter_values(prob)) != prob
+        gpo.obsfn(ps, current_time(prob))
+    else
+        gpo.obsfn(prob, nothing)
+    end
 end
 function (gpo::GetParameterObserved)(buffer::AbstractArray, ::NotTimeseries, prob)
-    gpo.obsfn(buffer, parameter_values(prob), current_time(prob))
+    if hasmethod(parameter_values, Tuple{typeof(prob)}) &&
+       (ps = parameter_values(prob)) != prob
+        gpo.obsfn(buffer, ps, current_time(prob))
+    else
+        gpo.obsfn(buffer, prob, nothing)
+    end
     return buffer
 end
 function (gpo::GetParameterObserved)(::Timeseries, prob)
diff --git a/test/parameter_indexing_test.jl b/test/parameter_indexing_test.jl
index b2347b29..43d6f5dc 100644
--- a/test/parameter_indexing_test.jl
+++ b/test/parameter_indexing_test.jl
@@ -130,6 +130,40 @@ for sys in [
             end
         end
 
+        for (sym, val, check_inference) in [
+            (:(a + b), p[1] + p[2], true),
+            ([:(a + b), :(a * b)], [p[1] + p[2], p[1] * p[2]], true),
+            ((:(a + b), :(a * b)), (p[1] + p[2], p[1] * p[2]), true),
+            ([:(a + c), :(a + b)], [p[1] + p[3], p[1] + p[2]], true)
+        ]
+            get = getp(sys, sym)
+            if check_inference
+                @inferred get(parameter_values(fi))
+            end
+            @test get(parameter_values(fi)) == val
+            if sym isa Union{Array, Tuple}
+                buffer = zeros(length(sym))
+                if check_inference
+                    @inferred get(buffer, parameter_values(fi))
+                else
+                    get(buffer, parameter_values(fi))
+                end
+                @test buffer == collect(val)
+            end
+        end
+
+        for sym in [
+            :(a + t),
+            [:(a + t), :(a * b)],
+            (:(a + t), :(a * b))
+        ]
+            get = getp(sys, sym)
+            @test_throws MethodError get(parameter_values(fi))
+            if sym isa Union{Array, Tuple}
+                @test_throws MethodError get(zeros(length(sym)), parameter_values(fi))
+            end
+        end
+
         getter = getp(sys, [])
         @test getter(fi) == []
         getter = getp(sys, ())