diff --git a/fastapi/_compat/v2.py b/fastapi/_compat/v2.py
index 777a22281..3936cd248 100644
--- a/fastapi/_compat/v2.py
+++ b/fastapi/_compat/v2.py
@@ -44,7 +44,12 @@ evaluate_forwardref = eval_type_lenient
 class GenerateJsonSchema(_GenerateJsonSchema):
     def bytes_schema(self, schema: CoreSchema) -> JsonSchemaValue:
         json_schema = {"type": "string", "contentMediaType": "application/octet-stream"}
-        if self._config.ser_json_bytes == "base64":
+        bytes_mode = (
+            self._config.ser_json_bytes
+            if self.mode == "serialization"
+            else self._config.val_json_bytes
+        )
+        if bytes_mode == "base64":
             json_schema["contentEncoding"] = "base64"
         self.update_with_validations(json_schema, schema, self.ValidationsMapping.bytes)
         return json_schema