diff --git a/src/Encoder/XsiTypeEncoder.php b/src/Encoder/XsiTypeEncoder.php
index b2d2954..e060ac5 100644
--- a/src/Encoder/XsiTypeEncoder.php
+++ b/src/Encoder/XsiTypeEncoder.php
@@ -25,35 +25,46 @@ public function __construct(
      */
     public function iso(Context $context): Iso
     {
+        $innerIso = $this->encoder->iso($context);
+
         return new Iso(
-            function (mixed $value) use ($context) : string {
-                return $this->to($context, $value);
+            function (mixed $value) use ($innerIso) : string {
+                return $this->to($innerIso, $value);
             },
-            function (string|Element $value) use ($context) : mixed {
+            function (string|Element $value) use ($context, $innerIso) : mixed {
                 return $this->from(
                     $context,
+                    $innerIso,
                     ($value instanceof Element ? $value : Element::fromString(non_empty_string()->assert($value)))
                 );
             }
         );
     }
 
-    private function to(Context $context, mixed $value): string
+    /**
+     * @param Iso<mixed, string> $innerIso
+     */
+    private function to(Iso $innerIso, mixed $value): string
     {
         // There is no way to know what xsi:type to use when encoding any type.
         // The type defined in the wsdl will always be used to encode the value.
         // If you want more control over the encoded type, please control how to encode by using the MatchingValueEncoder.
-        return $this->encoder->iso($context)->to($value);
+        return $innerIso->to($value);
     }
 
-    private function from(Context $context, Element $value): mixed
+    /**
+     * @param Iso<mixed, string> $innerIso
+     */
+    private function from(Context $context, Iso $innerIso, Element $value): mixed
     {
-        /** @var XmlEncoder<string, mixed> $encoder */
-        $encoder = match (true) {
-            $this->encoder instanceof Feature\DisregardXsiInformation => $this->encoder,
-            default => XsiTypeDetector::detectEncoderFromXmlElement($context, $value->element())->unwrapOr($this->encoder)
+        $iso = match (true) {
+            $this->encoder instanceof Feature\DisregardXsiInformation => $innerIso,
+            default => XsiTypeDetector::detectEncoderFromXmlElement($context, $value->element())
+                ->map(static fn (XmlEncoder $encoder): Iso => $encoder->iso($context))
+                ->unwrapOr($innerIso),
         };
 
-        return $encoder->iso($context)->from($value);
+        /** @psalm-suppress ImplicitToStringCast - Encoders accept string|Element in from() */
+        return $iso->from($value);
     }
 }