diff --git a/src/systems/index_cache.jl b/src/systems/index_cache.jl
index 4fc2f18bfd..623623da42 100644
--- a/src/systems/index_cache.jl
+++ b/src/systems/index_cache.jl
@@ -404,6 +404,7 @@ function SymbolicIndexingInterface.timeseries_parameter_index(ic::IndexCache, sy
         sym = get(ic.symbol_to_variable, sym, nothing)
         sym === nothing && return nothing
     end
+    sym = unwrap(sym)
     idx = check_index_map(ic.discrete_idx, sym)
     idx === nothing ||
         return ParameterTimeseriesIndex(idx.clock_idx, (idx.buffer_idx, idx.idx_in_clock))
@@ -411,7 +412,8 @@ function SymbolicIndexingInterface.timeseries_parameter_index(ic::IndexCache, sy
     args = arguments(sym)
     idx = timeseries_parameter_index(ic, args[1])
     idx === nothing && return nothing
-    ParameterIndex(idx.portion, (idx.idx..., args[2:end]...), idx.validate_size)
+    return ParameterTimeseriesIndex(
+        idx.timeseries_idx, (idx.parameter_idx..., args[2:end]...))
 end
 
 function check_index_map(idxmap, sym)
diff --git a/test/symbolic_indexing_interface.jl b/test/symbolic_indexing_interface.jl
index e46c197dde..4a7cd926b4 100644
--- a/test/symbolic_indexing_interface.jl
+++ b/test/symbolic_indexing_interface.jl
@@ -224,3 +224,14 @@ end
     end
     @test isempty(get_all_timeseries_indexes(sys, a))
 end
+
+@testset "`timeseries_parameter_index` on unwrapped scalarized timeseries parameter" begin
+    @variables x(t)[1:2]
+    @parameters p(t)[1:2, 1:2]
+    ev = [x[1] ~ 2.0] => [p ~ -ones(2, 2)]
+    @mtkbuild sys = ODESystem(D(x) ~ p * x, t; continuous_events = [ev])
+    p = ModelingToolkit.unwrap(p)
+    @test timeseries_parameter_index(sys, p) === ParameterTimeseriesIndex(1, (1, 1))
+    @test timeseries_parameter_index(sys, p[1, 1]) ===
+          ParameterTimeseriesIndex(1, (1, 1, 1, 1))
+end