diff --git a/Project.toml b/Project.toml
index af66226..0520c19 100644
--- a/Project.toml
+++ b/Project.toml
@@ -13,6 +13,15 @@ Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 StatsBase = "2913bbd2-ae8a-5f71-8c99-4fb6c76f3a91"
 StatsFuns = "4c63d2b9-4356-54db-8cca-17b64c39e42c"
 
+[weakdeps]
+Optim = "429524aa-4258-5aef-a3af-852621145aeb"
+
+[extras]
+Optim = "429524aa-4258-5aef-a3af-852621145aeb"
+
+[extensions]
+DistributionFitsOptimExt = "Optim"
+
 [compat]
 Distributions = "0.25"
 FillArrays = "0.12, 0.13"
@@ -22,3 +31,5 @@ StaticArrays = "1.2"
 StatsBase = "0.33"
 StatsFuns = "0.9, 1"
 julia = "1.6"
+Optim = "1.7"
+
diff --git a/ext/DistributionFitsOptimExt.jl b/ext/DistributionFitsOptimExt.jl
new file mode 100644
index 0000000..84c1217
--- /dev/null
+++ b/ext/DistributionFitsOptimExt.jl
@@ -0,0 +1,19 @@
+module DistributionFitsOptimExt
+
+isdefined(Base, :get_extension) ? (using Optim) : (using ..Optim)
+using DistributionFits: DistributionFits, optimize, AbstractDistributionFitOptimizer
+
+struct OptimOptimizer <:  AbstractDistributionFitOptimizer; end
+
+function DistributionFits.optimize(f, ::OptimOptimizer, lower, upper) 
+    result = Optim.optimize(f, lower, upper)
+    (;minimizer = result.minimizer, converged = result.converged, result)
+end
+
+function __init__()
+    @info "DistributionFits: setting OptimOptimizer"
+    #DistributionFits.set_optimizer(DistributionFitsOptimExt.OptimOptimizer())
+    DistributionFits.set_optimizer(OptimOptimizer())
+end
+
+end
\ No newline at end of file
diff --git a/src/DistributionFits.jl b/src/DistributionFits.jl
index 2359c8f..34e288b 100644
--- a/src/DistributionFits.jl
+++ b/src/DistributionFits.jl
@@ -5,7 +5,10 @@ using Reexport
 
 using FillArrays, StaticArrays
 using StatsFuns: logit, logistic, normcdf
-using Requires: @require 
+
+if !isdefined(Base, :get_extension)
+  using Requires
+end
 
 # for extension
 import Distributions: mean, var, mode
@@ -21,6 +24,11 @@ export
   @qs_cf90, @qs_cf95,
   fit_mean_relerror
 
+# document but do not export - need to qualify by 'DistributionFits.'
+# export
+#   # Optimizer detail
+#   optimize, set_optimizer  
+
 # LogNormal
 export AbstractΣstar, Σstar, σstar
 
@@ -30,11 +38,13 @@ export fit_mode_flat, shifloNormal
 # dependency inversion: need to define DistributionFits.optimize by user
 export AbstractDistributionFitOptimizer, optimize
 
-
 include("optimizer.jl")
 
+
 function __init__()
-  @require Optim="429524aa-4258-5aef-a3af-852621145aeb" include("requires_optim.jl")
+  @static if !isdefined(Base, :get_extension)
+    @require Optim="429524aa-4258-5aef-a3af-852621145aeb" include("../ext/DistributionFitsOptimExt.jl")
+  end
 end
 
 # fitting distributions to stats
diff --git a/src/optimizer.jl b/src/optimizer.jl
index a899c02..1a52a38 100644
--- a/src/optimizer.jl
+++ b/src/optimizer.jl
@@ -11,7 +11,8 @@ function `f` on bounded interval `[lower,upper]`:
 Returning an object with fields `minimizer` and `converged`.
 
 `DistributionFits.set_optimizer(::AbstractDistributionFitOptimizer)` 
-sets the optimizer used in calling the optimize function. 
+sets the specific AbstractDistributionFitOptimizer that is used 
+throughout the package for calling the optimize function. 
 Specializing this function with a concrete type, allows using different
 optimization packages. 
 
@@ -20,21 +21,25 @@ package is in scope, the
 `OptimOptimizer` is set, which implements the interface by using Optim's 
 [optimize](https://julianlsolvers.github.io/Optim.jl/stable/#user/minimization/#minimizing-a-univariate-function-on-a-bounded-interval) function.
 
-Hence, the module using DistribuitonFits.jl has to either
+Hence, the module using `DistributionFits.jl` has to either
 
 - explicitly invoke `using Optim`, or
 - call `set_optimizer` with the concrete subtype of `AbstractDistributionFitOptimizer`
-  for which the corresponding optimize method is implemented.
+  for which the corresponding `optimize` method is implemented. 
+    
+Developers implementing usage of a different specific optimizer see code in 
+ext/DistributionFitsOptimExt.
 """
 abstract type AbstractDistributionFitOptimizer end
-struct OptimOptimizer <:  AbstractDistributionFitOptimizer; end
 struct NotSetOptimizer <: AbstractDistributionFitOptimizer; end
 
+# see to ext/DistributionFitsOptimExt.jl
 
 optimize(f, ::NotSetOptimizer, lower, upper) = error(
     "Optimizer not set yet. Either invoke 'using Optim' or 'DistributionFits.set_optimizer(...)'.")
 
 
-optimizer = NotSetOptimizer();
-optimize(f, lower, upper) = optimize(f, optimizer, lower, upper)
-set_optimizer(opt::AbstractDistributionFitOptimizer) = (global optimizer = opt)
+df_optimizer = NotSetOptimizer();
+optimize(f, lower, upper) = optimize(f, df_optimizer, lower, upper)
+set_optimizer(opt::AbstractDistributionFitOptimizer) = (global df_optimizer = opt)
+
diff --git a/src/requires_optim.jl b/src/requires_optim.jl
deleted file mode 100644
index ec28fe3..0000000
--- a/src/requires_optim.jl
+++ /dev/null
@@ -1,7 +0,0 @@
-function optimize(f, ::OptimOptimizer, lower, upper) 
-    result = Optim.optimize(f, lower, upper)
-    (;minimizer = result.minimizer, converged = result.converged, result)
-end
-
-@info "DistributionFits: setting OptimOptimizer"
-DistributionFits.set_optimizer(OptimOptimizer())
diff --git a/test/runtests.jl b/test/runtests.jl
index 46f2db8..7d868fe 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -3,16 +3,20 @@ using Test
 using Random: Random
 
 @testset "optimize error" begin
-    @test_throws Exception DistributionFits.optimize(x -> x*x, DistributionFits.optimizer, -1, 1)
+    @test_throws Exception DistributionFits.optimize(x -> x*x, -1, 1)
 end
 # Optim package for interactive testing
 i_loadlibs = () -> begin
     push!(LOAD_PATH, expanduser("~/julia/scimltools/")) # access local package repo
+    push!(LOAD_PATH, expanduser("~/julia/18_tools/scimltools/")) # access local package repo
 end
 using Optim: Optim, optimize
+
+DistributionFitsOptimExt = isdefined(Base, :get_extension) ? Base.get_extension(DistributionFits, :DistributionFitsOptimExt) : DistributionFits.DistributionFitsOptimExt
+
 @testset "optimize set in __init__ after using Optim" begin
     # set in __init__
-    @test DistributionFits.optimizer isa DistributionFits.OptimOptimizer
+    @test DistributionFits.df_optimizer isa DistributionFitsOptimExt.OptimOptimizer
 end
 
 const tests = [