diff --git a/base/boot.jl b/base/boot.jl
index 1933e511210c5..cd3ae8b4909bb 100644
--- a/base/boot.jl
+++ b/base/boot.jl
@@ -236,7 +236,7 @@ eval(m::Module, e::ANY) = ccall(:jl_toplevel_eval_in, Any, (Any, Any), m, e)
 
 kwfunc(f::ANY) = ccall(:jl_get_keyword_sorter, Any, (Any,), f)
 
-kwftype(t::ANY) = typeof(ccall(:jl_get_kwsorter, Any, (Any,), t.name))
+kwftype(t::ANY) = typeof(ccall(:jl_get_kwsorter, Any, (Any,), t))
 
 mutable struct Box
     contents::Any
diff --git a/src/dump.c b/src/dump.c
index 7959f4c390b60..f227cc674c73e 100644
--- a/src/dump.c
+++ b/src/dump.c
@@ -1366,7 +1366,7 @@ static jl_value_t *jl_deserialize_datatype(jl_serializer_state *s, int pos, jl_v
     }
     if (tag == 9) {
         jl_datatype_t *primarydt = (jl_datatype_t*)jl_deserialize_value(s, NULL);
-        jl_value_t *dtv = jl_typeof(jl_get_kwsorter(primarydt->name));
+        jl_value_t *dtv = jl_typeof(jl_get_kwsorter((jl_value_t*)primarydt));
         backref_list.items[pos] = dtv;
         return dtv;
     }
diff --git a/src/gf.c b/src/gf.c
index 84a2bcb3923dc..79b6ea7ca7567 100644
--- a/src/gf.c
+++ b/src/gf.c
@@ -2402,8 +2402,12 @@ jl_function_t *jl_new_generic_function_with_supertype(jl_sym_t *name, jl_module_
     return (jl_function_t*)f;
 }
 
-JL_DLLEXPORT jl_function_t *jl_get_kwsorter(jl_typename_t *tn)
+JL_DLLEXPORT jl_function_t *jl_get_kwsorter(jl_value_t *ty)
 {
+    jl_datatype_t *dt = jl_argument_datatype(ty);
+    if (dt == NULL)
+        jl_error("cannot get keyword sorter for abstract type");
+    jl_typename_t *tn = dt->name;
     jl_methtable_t *mt = tn->mt;
     if (!mt->kwsorter) {
         JL_LOCK(&mt->writelock);
diff --git a/src/julia.h b/src/julia.h
index 89ee52892a7d8..fbb9e8ea0ad14 100644
--- a/src/julia.h
+++ b/src/julia.h
@@ -1038,7 +1038,7 @@ JL_DLLEXPORT void jl_method_def(jl_svec_t *argdata, jl_code_info_t *f, jl_value_
 JL_DLLEXPORT jl_code_info_t *jl_code_for_staged(jl_method_instance_t *linfo);
 JL_DLLEXPORT jl_code_info_t *jl_copy_code_info(jl_code_info_t *src);
 JL_DLLEXPORT size_t jl_get_world_counter(void);
-JL_DLLEXPORT jl_function_t *jl_get_kwsorter(jl_typename_t *tn);
+JL_DLLEXPORT jl_function_t *jl_get_kwsorter(jl_value_t *ty);
 JL_DLLEXPORT jl_value_t *jl_box_bool(int8_t x);
 JL_DLLEXPORT jl_value_t *jl_box_int8(int8_t x);
 JL_DLLEXPORT jl_value_t *jl_box_uint8(uint8_t x);
diff --git a/src/julia_internal.h b/src/julia_internal.h
index 135d6c5655021..1d7c4ecd171a7 100644
--- a/src/julia_internal.h
+++ b/src/julia_internal.h
@@ -375,6 +375,7 @@ jl_method_instance_t *jl_method_lookup(jl_methtable_t *mt, jl_value_t **args, si
 jl_value_t *jl_gf_invoke(jl_tupletype_t *types, jl_value_t **args, size_t nargs);
 
 JL_DLLEXPORT jl_datatype_t *jl_first_argument_datatype(jl_value_t *argtypes);
+jl_datatype_t *jl_argument_datatype(jl_value_t *argt);
 
 jl_value_t *jl_nth_slot_type(jl_value_t *sig, size_t i);
 void jl_compute_field_offsets(jl_datatype_t *st);
diff --git a/src/method.c b/src/method.c
index 40fe7ec9ff31e..d9b98aecd1f8f 100644
--- a/src/method.c
+++ b/src/method.c
@@ -576,6 +576,12 @@ JL_DLLEXPORT jl_datatype_t *jl_first_argument_datatype(jl_value_t *argtypes)
     return first_arg_datatype(argtypes, 0);
 }
 
+// get DataType implied by a single given type
+jl_datatype_t *jl_argument_datatype(jl_value_t *argt)
+{
+    return first_arg_datatype(argt, 1);
+}
+
 extern tracer_cb jl_newmeth_tracer;
 JL_DLLEXPORT void jl_method_def(jl_svec_t *argdata,
                                 jl_code_info_t *f,
diff --git a/test/keywordargs.jl b/test/keywordargs.jl
index e724448d88374..e3806fc87509f 100644
--- a/test/keywordargs.jl
+++ b/test/keywordargs.jl
@@ -248,3 +248,13 @@ f7045(x::Real; y=true) = y ? 2 : 3
 @test f7045(1.0) === 1
 @test f7045(1, y=false) === 3
 @test f7045(1.0, y=false) === 3
+
+# issue #20804
+struct T20804{T}
+    y::T
+end
+(f::T20804)(;x=10) = f.y + x
+let x = T20804(4)
+    @test x() == 14
+    @test x(x=8) == 12
+end