diff --git a/src/plugins/documenter.jl b/src/plugins/documenter.jl
index 97ae7dc..b52eee8 100644
--- a/src/plugins/documenter.jl
+++ b/src/plugins/documenter.jl
@@ -33,14 +33,22 @@ function gen_plugin(p::Documenter, t::Template, pkg_name::AbstractString)
     end
 
     kwargs_string = if :additional_kwargs in fieldnames(typeof(p))
-        set_kwargs = ["modules", "format", "pages", "repo", "sitename", "authors", "assets"]
+        standard_kwargs = ["modules", "format", "pages", "repo", "sitename", "authors", "assets"]
 
         # We want something that looks like the following:
         #     key1="val1",
         #     key2="val2",
         #
-        kwargs = (x for x in p.additional_kwargs if first(x) ∉ set_kwargs)
-        join(string(tab, first(p), "=", repr(last(p)), ",\n") for p in kwargs)
+        valid_keys = [k for k in keys(p.additional_kwargs) if k ∉ standard_kwargs]
+        if length(p.additional_kwargs) > length(valid_keys)
+            invalid_keys = (repr(k) for k in keys(p.additional_kwargs) if k in standard_kwargs)
+            @warn string(
+                "Ignoring predefined Documenter kwargs ",
+                join(invalid_keys, ", "),
+                " from additional kwargs."
+            )
+        end
+        join(string(tab, k, "=", repr(p.additional_kwargs[k]), ",\n") for k in valid_keys)
     else
         ""
     end
diff --git a/test/tests.jl b/test/tests.jl
index aca2855..378a3d0 100644
--- a/test/tests.jl
+++ b/test/tests.jl
@@ -13,11 +13,6 @@ end
 struct Bar <: CustomPlugin end
 # A dummy Plugin subtype.
 struct Baz <: Plugin end
-# A Documenter with extra kwargs
-struct Bat <: Documenter
-    assets::Vector{AbstractString}
-    additional_kwargs::Vector{<:Pair}
-end
 
 # Various options to be passed into templates.
 const me = "christopher-dG"
@@ -402,19 +397,25 @@ end
     include(joinpath("plugins", "githubpages.jl"))
 end
 
+# A Documenter with extra kwargs
+struct Qux <: Documenter
+    assets::Vector{AbstractString}
+    additional_kwargs::AbstractDict
+end
 @testset "Documenter add kwargs" begin
     t = Template(; user=me)
     pkg_dir = joinpath(t.dir, test_pkg)
-    p = Bat(
+    p = Qux(
         [],
-        ["strict"=>true, "checkdocs"=>:none, "format"=>:markdown, "stringarg"=>"string"]
+        Dict("strict"=>true, "checkdocs"=>:none, "format"=>:markdown, "stringarg"=>"string")
     )
-    gen_plugin(p, t, test_pkg)
+    warn_str = "Ignoring predefined Documenter kwargs \"format\" from additional kwargs."
+    @test_logs (:warn, warn_str) gen_plugin(p, t, test_pkg)
     make = readchomp(joinpath(pkg_dir, "docs", "make.jl"))
     @test occursin(
         strip("""
-            strict=true,
             checkdocs=:none,
+            strict=true,
             stringarg="string",
         """),
         make,