diff --git a/src/call_plots.jl b/src/call_plots.jl
index ace2451..d9b2719 100644
--- a/src/call_plots.jl
+++ b/src/call_plots.jl
@@ -158,7 +158,11 @@ plot = plot_demand(res)
 - `title::String`: Set a title for the plots
 - `horizon::Int64`: To plot a shorter window of time than the full results
 - `initial_time::DateTime`: To start the plot at a different time other than the results initial time
-- `aggregate::String = "System", "PowerLoad", or "Bus"`: aggregate the demand other than by generator
+- `aggregation::Type = PowerSystems.StaticLoad`: aggregate the demand by
+    [`PowerSystems.System`](@extref), [`PowerSystems.ACBus`](@extref), a `PowerSystems.StaticLoad`
+    subtype such as [`PowerSystems.PowerLoad`](@extref), or a `PowerSystems.AggregationTopology`
+    subtype. Only applies when plotting a [`PowerSystems.System`](@extref).
+- `aggregate::String`: convenience alias for `aggregation`: `"System"`, `"Bus"`, or `"PowerLoad"`
 - `set_display::Bool = true`: set to false to prevent the plots from displaying
 - `save::String = "file_path"`: set a file path to save the plots
 - `format::String = "png"`: file extension for saved plots. CairoMakie supports `"png"`, `"pdf"`, `"svg"`. PlotlyLight only supports `"html"` (other values are written as `.html` with a warning).
@@ -271,9 +275,11 @@ instead of CairoMakie.
 - `title::String`: Set a title for the plots
 - `horizon::Int64`: To plot a shorter window of time than the full results
 - `initial_time::DateTime`: To start the plot at a different time other than the results initial time
-- `aggregate::String = "System", "PowerLoad", or "Bus"`: aggregate the demand by
-    [`PowerSystems.System`](@extref), [`PowerSystems.PowerLoad`](@extref), or [`PowerSystems.Bus`](@extref),
-    rather than by generator
+- `aggregation::Type = PowerSystems.StaticLoad`: aggregate the demand by
+    [`PowerSystems.System`](@extref), [`PowerSystems.ACBus`](@extref), a `PowerSystems.StaticLoad`
+    subtype such as [`PowerSystems.PowerLoad`](@extref), or a `PowerSystems.AggregationTopology`
+    subtype. Only applies when plotting a [`PowerSystems.System`](@extref).
+- `aggregate::String`: convenience alias for `aggregation`: `"System"`, `"Bus"`, or `"PowerLoad"`
 - `set_display::Bool = true`: set to false to prevent the plots from displaying
 - `save::String = "file_path"`: set a file path to save the plots
 - `format::String = "png"`: file extension for saved plots. CairoMakie supports `"png"`, `"pdf"`, `"svg"`. PlotlyLight only supports `"html"` (other values are written as `.html` with a warning).
diff --git a/test/test_demand_aggregation.jl b/test/test_demand_aggregation.jl
new file mode 100644
index 0000000..e5c56b1
--- /dev/null
+++ b/test/test_demand_aggregation.jl
@@ -0,0 +1,35 @@
+@testset "demand aggregation keyword" begin
+    for (str, type) in
+        ("System" => PSY.System, "Bus" => PSY.ACBus, "PowerLoad" => PSY.PowerLoad)
+        translated = PG._translate_demand_aggregate(Dict(:aggregate => str))
+        @test translated[:aggregation] === type
+        @test !haskey(translated, :aggregate)
+    end
+
+    # Issue #126: a typed `aggregation` passed directly must reach PowerAnalytics untouched,
+    # without disturbing the other keywords.
+    passthrough =
+        PG._translate_demand_aggregate(Dict(:aggregation => PSY.ACBus, :title => "demand"))
+    @test passthrough[:aggregation] === PSY.ACBus
+    @test passthrough[:title] == "demand"
+
+    # A type given under the legacy `aggregate` name is forwarded, not stringified.
+    @test PG._translate_demand_aggregate(Dict(:aggregate => PSY.ACBus))[:aggregation] ===
+          PSY.ACBus
+
+    # `aggregate = nothing` means "no aggregation": PowerAnalytics keeps its own default.
+    @test !haskey(PG._translate_demand_aggregate(Dict(:aggregate => nothing)), :aggregation)
+
+    @test_throws ArgumentError PG._translate_demand_aggregate(Dict(:aggregate => "bus"))
+
+    # `PA.get_load_data(::PSY.System)` only aggregates over `PSY.System`, `PSY.ACBus`,
+    # `StaticLoad` subtypes and `AggregationTopology` subtypes, so every type the table
+    # maps to has to fall in that set. "System" and "Bus" are also covered end to end in
+    # test_plot_creation.jl; this catches "PowerLoad" and any entry added later.
+    @test all(
+        t ->
+            t in (PSY.System, PSY.ACBus) ||
+                t <: Union{PSY.StaticLoad, PSY.AggregationTopology},
+        values(PG._AGGREGATE_STRING_TO_TYPE),
+    )
+end
diff --git a/test/test_plot_creation.jl b/test/test_plot_creation.jl
index 69cf878..23a8b1f 100644
--- a/test/test_plot_creation.jl
+++ b/test/test_plot_creation.jl
@@ -267,6 +267,17 @@ function test_plots(file_path::String; backend_pkg::String = "cairomakie")
         plot_length = backend_pkg == "cairomakie" ? p.series_count : length(p.data)
         @test plot_length == 3
 
+        # Issue #126: the typed `aggregation` keyword must survive to `get_load_data`.
+        # Not saved, so the expected file list below is unchanged.
+        p = plot_demand_fn(
+            sys_with_ts;
+            set_display = set_display,
+            title = "sysdemand_aggregation",
+            aggregation = ACBus,
+        )
+        plot_length = backend_pkg == "cairomakie" ? p.series_count : length(p.data)
+        @test plot_length == 3
+
         list = readdir(out_path)
         # PlotlyLight only supports HTML export, CairoMakie supports PNG
         file_ext = backend_pkg == "plotlylight" ? ".html" : ".png"