diff --git a/src/core/Encoding/Builtin.pm6 b/src/core/Encoding/Builtin.pm6
index 42b22b4b1de..9ba026e3192 100644
--- a/src/core/Encoding/Builtin.pm6
+++ b/src/core/Encoding/Builtin.pm6
@@ -16,9 +16,10 @@ class Encoding::Builtin does Encoding {
 
     method alternative-names() { $!alternative-names }
 
-    method decoder(*%options --> Encoding::Decoder) {
-        %options<replacement> = self!rep-char(%options<replacement>) if %options<replacement>:exists && %options<replacement>.DEFINITE && %options<replacement> !=== False;
-        Encoding::Decoder::Builtin.new($!name, |%options)
+    method decoder(:$replacement, :$translate-nl, :$strict --> Encoding::Decoder) {
+        my $decoder = $replacement.DEFINITE && $replacement !=== False
+            ?? Encoding::Decoder::Builtin.new($!name, :$strict, :$translate-nl, :replacement(self!rep-char($replacement)))
+            !! Encoding::Decoder::Builtin.new($!name, :$strict, :$translate-nl);
     }
 
     my int $is-win = Rakudo::Internals.IS-WIN;
diff --git a/src/core/Encoding/Decoder/Builtin.pm6 b/src/core/Encoding/Decoder/Builtin.pm6
index 870e0cbbb60..8de90e2a1bd 100644
--- a/src/core/Encoding/Decoder/Builtin.pm6
+++ b/src/core/Encoding/Decoder/Builtin.pm6
@@ -1,9 +1,9 @@
 my class Encoding::Decoder::Builtin is repr('Decoder') does Encoding::Decoder {
-    method new(str $encoding, :$translate-nl, Str :$replacement, Bool:D :$strict = False) {
+    method new(str $encoding, :$translate-nl, :$replacement, :$strict) {
         nqp::decoderconfigure(nqp::create(self), $encoding,
             nqp::hash(
                 'translate_newlines', $translate-nl ?? 1 !! 0,
-                'replacement', $replacement.defined ?? nqp::unbox_s($replacement) !! nqp::null(),
+                'replacement', $replacement.defined ?? nqp::unbox_s($replacement) !! nqp::null_s(),
                 'config', $strict ?? 0 !! 1
                 # Config set to 0 uses the decoder's new default, which is strict
                 # decoding. Setting to 1 uses the 6.c specced functionality where