diff --git a/zerver/lib/request.py b/zerver/lib/request.py
index 84f74414ab..989f5818a4 100644
--- a/zerver/lib/request.py
+++ b/zerver/lib/request.py
@@ -31,6 +31,7 @@ import zerver.tornado.handlers as handlers
 from zerver.lib.exceptions import ErrorCode, InvalidJSONError, JsonableError
 from zerver.lib.notes import BaseNotes
 from zerver.lib.types import Validator, ViewFuncT
+from zerver.lib.validator import check_anything
 from zerver.models import Client, Realm
 
 
@@ -168,6 +169,10 @@ class _REQ(Generic[ResultT]):
 
         """
 
+        if argument_type == "body" and converter is None and json_validator is None:
+            # legacy behavior
+            json_validator = cast(Callable[[str, object], ResultT], check_anything)
+
         self.post_var_name = whence
         self.func_var_name: Optional[str] = None
         self.converter = converter
@@ -206,6 +211,7 @@ def REQ(
     *,
     converter: Callable[[str, str], ResultT],
     default: ResultT = ...,
+    argument_type: Optional[Literal["body"]] = ...,
     intentionally_undocumented: bool = ...,
     documentation_pending: bool = ...,
     aliases: Sequence[str] = ...,
@@ -221,6 +227,7 @@ def REQ(
     *,
     default: ResultT = ...,
     json_validator: Validator[ResultT],
+    argument_type: Optional[Literal["body"]] = ...,
     intentionally_undocumented: bool = ...,
     documentation_pending: bool = ...,
     aliases: Sequence[str] = ...,
@@ -368,46 +375,45 @@ def has_request_variables(view_func: ViewFuncT) -> ViewFuncT:
                 continue
             assert func_var_name is not None
 
+            post_var_name: Optional[str]
+
             if param.argument_type == "body":
+                post_var_name = "request"
                 try:
-                    val = orjson.loads(request.body)
-                except orjson.JSONDecodeError:
-                    raise InvalidJSONError(_("Malformed JSON"))
-                kwargs[func_var_name] = val
-                continue
+                    val = request.body.decode(request.encoding or "utf-8")
+                except UnicodeDecodeError:
+                    raise JsonableError(_("Malformed payload"))
             else:
                 # This is a view bug, not a user error, and thus should throw a 500.
                 assert param.argument_type is None, "Invalid argument type"
 
-            post_var_names = [param.post_var_name]
-            post_var_names += param.aliases
+                post_var_names = [param.post_var_name]
+                post_var_names += param.aliases
+                post_var_name = None
 
-            post_var_name: Optional[str] = None
-
-            for req_var in post_var_names:
-                assert req_var is not None
-                if req_var in request.POST:
-                    val = request.POST[req_var]
-                    request_notes.processed_parameters.add(req_var)
-                elif req_var in request.GET:
-                    val = request.GET[req_var]
-                    request_notes.processed_parameters.add(req_var)
-                else:
-                    # This is covered by test_REQ_aliases, but coverage.py
-                    # fails to recognize this for some reason.
-                    continue  # nocoverage
-                if post_var_name is not None:
+                for req_var in post_var_names:
                     assert req_var is not None
-                    raise RequestConfusingParmsError(post_var_name, req_var)
-                post_var_name = req_var
+                    if req_var in request.POST:
+                        val = request.POST[req_var]
+                        request_notes.processed_parameters.add(req_var)
+                    elif req_var in request.GET:
+                        val = request.GET[req_var]
+                        request_notes.processed_parameters.add(req_var)
+                    else:
+                        # This is covered by test_REQ_aliases, but coverage.py
+                        # fails to recognize this for some reason.
+                        continue  # nocoverage
+                    if post_var_name is not None:
+                        raise RequestConfusingParmsError(post_var_name, req_var)
+                    post_var_name = req_var
 
-            if post_var_name is None:
-                post_var_name = param.post_var_name
-                assert post_var_name is not None
-                if param.default is _REQ.NotSpecified:
-                    raise RequestVariableMissingError(post_var_name)
-                kwargs[func_var_name] = param.default
-                continue
+                if post_var_name is None:
+                    post_var_name = param.post_var_name
+                    assert post_var_name is not None
+                    if param.default is _REQ.NotSpecified:
+                        raise RequestVariableMissingError(post_var_name)
+                    kwargs[func_var_name] = param.default
+                    continue
 
             if param.converter is not None:
                 try:
@@ -422,6 +428,8 @@ def has_request_variables(view_func: ViewFuncT) -> ViewFuncT:
                 try:
                     val = orjson.loads(val)
                 except orjson.JSONDecodeError:
+                    if param.argument_type == "body":
+                        raise InvalidJSONError(_("Malformed JSON"))
                     raise JsonableError(_('Argument "{}" is not valid JSON.').format(post_var_name))
 
                 try:
diff --git a/zerver/lib/validator.py b/zerver/lib/validator.py
index c9138f71e4..7c080da2a3 100644
--- a/zerver/lib/validator.py
+++ b/zerver/lib/validator.py
@@ -58,6 +58,10 @@ from zerver.lib.types import ProfileFieldData, Validator
 ResultT = TypeVar("ResultT")
 
 
+def check_anything(var_name: str, val: object) -> object:
+    return val
+
+
 def check_string(var_name: str, val: object) -> str:
     if not isinstance(val, str):
         raise ValidationError(_("{var_name} is not a string").format(var_name=var_name))
diff --git a/zerver/tests/test_decorators.py b/zerver/tests/test_decorators.py
index 61b4500cab..1c0556e4f5 100644
--- a/zerver/tests/test_decorators.py
+++ b/zerver/tests/test_decorators.py
@@ -248,6 +248,12 @@ class DecoratorTestCase(ZulipTestCase):
         ) -> HttpResponse:
             return json_response(data={"payload": payload})
 
+        request = HostRequestMock()
+        request.body = b"\xde\xad\xbe\xef"
+        with self.assertRaises(JsonableError) as cm:
+            get_payload(request)
+        self.assertEqual(str(cm.exception), "Malformed payload")
+
         request = HostRequestMock()
         request.body = b"notjson"
         with self.assertRaises(JsonableError) as cm: