diff --git a/Project.toml b/Project.toml
index 0a76d1a7..a60e2031 100644
--- a/Project.toml
+++ b/Project.toml
@@ -13,13 +13,18 @@ LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 MLStyle = "d8e11817-5142-5d16-987a-aa16d5891078"
 MacroTools = "1914dd2f-81c6-5fcd-8719-6d5c9610ff09"
 Parameters = "d96e819e-fc66-5662-9728-84c9c7592b0a"
-Plots = "91a5bcdd-55d7-5caf-9e0b-520d859cae80"
 PrettyTables = "08abe8d2-0d0c-5749-adfa-8a2ac140af0d"
 Printf = "de0858da-6303-5e67-8744-51eddeeeb8d7"
 Reexport = "189a3867-3050-52da-a836-e630ba90ab69"
 ReplMaker = "b873ce64-0db9-51f5-a568-4457d8e49576"
 Unicode = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"
 
+[weakdeps]
+Plots = "91a5bcdd-55d7-5caf-9e0b-520d859cae80"
+
+[extensions]
+CTBasePlots = "Plots"
+
 [compat]
 DataStructures = "0.18"
 DifferentiationInterface = "0.5"
diff --git a/ext/CTBasePlots.jl b/ext/CTBasePlots.jl
new file mode 100644
index 00000000..dd1e540e
--- /dev/null
+++ b/ext/CTBasePlots.jl
@@ -0,0 +1,16 @@
+module CTBasePlots
+
+    #
+    using DocStringExtensions
+    using MLStyle # pattern matching
+
+    #
+    using CTBase
+    using Plots
+    using LinearAlgebra
+    import Plots: plot, plot!
+
+    # --------------------------------------------------------------------------------------------------
+    include("plot.jl")
+
+end
\ No newline at end of file
diff --git a/src/plot.jl b/ext/plot.jl
similarity index 98%
rename from src/plot.jl
rename to ext/plot.jl
index 5f5861ac..244424aa 100644
--- a/src/plot.jl
+++ b/ext/plot.jl
@@ -11,8 +11,8 @@ $(TYPEDEF)
 A leaf of a plot tree.
 """
 struct PlotLeaf <: AbstractPlotTreeElement
-    value::Tuple{Symbol,Integer}
-    PlotLeaf(value::Tuple{Symbol,Integer}) = new(value) 
+    value::Tuple{Symbol, Integer}
+    PlotLeaf(value::Tuple{Symbol, Integer}) = new(value) 
 end
 
 """
@@ -402,7 +402,7 @@ function Plots.plot(sol::OptimalControlSolution;
     #
     p = __initial_plot(sol; layout=layout, control=control, size=size, kwargs...)
     #
-    return plot!(p, sol; layout=layout, control=control, time=time, solution_label=solution_label,
+    return Plots.plot!(p, sol; layout=layout, control=control, time=time, solution_label=solution_label,
         state_style=state_style, control_style=control_style, costate_style=costate_style, kwargs...)
 end
 
diff --git a/src/CTBase.jl b/src/CTBase.jl
index 7bd265b1..64dc27ef 100644
--- a/src/CTBase.jl
+++ b/src/CTBase.jl
@@ -19,7 +19,6 @@ import ForwardDiff
 using Interpolations: linear_interpolation, Line, Interpolations # for default interpolation
 using MLStyle # pattern matching
 using Parameters # @with_kw: to have default values in struct
-using Plots
 using Printf # to print an Opt imalControlModel
 using DataStructures # OrderedDict for aliases
 using Unicode # unicode primitives
@@ -205,7 +204,6 @@ include("utils.jl")
 include("checking.jl")
 #
 include("print.jl")
-include("plot.jl")
 #
 include("functions.jl")
 include("model.jl")
@@ -256,7 +254,6 @@ export dim_boundary_conditions, dim_control_constraints, dim_state_constraints,
 
 # solution
 export OptimalControlSolution
-export plot, plot!
 
 # initialization
 export OptimalControlInit
diff --git a/test/test_plot_joseph.jl b/test/test_plot_joseph.jl
index fcb5c708..4908c9bc 100644
--- a/test/test_plot_joseph.jl
+++ b/test/test_plot_joseph.jl
@@ -17,6 +17,7 @@
 
 # a la main
 using CTBase
+using PlotUtils
 
 n=1
 m=1
diff --git a/test/test_plot_manual.jl b/test/test_plot_manual.jl
index e1467443..fbd67c01 100644
--- a/test/test_plot_manual.jl
+++ b/test/test_plot_manual.jl
@@ -1,5 +1,5 @@
 using CTBase
-#using Plots
+using Plots
 
 layout = :split
 size   = (900, 600)