diff --git a/CHANGELOG.md b/CHANGELOG.md
index a01135930..a63fc1e0d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,7 +26,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  - #2236, Support POSIX regular expression operators for row filtering - @enote-kane
  - #2202, Allow returning XML from RPCs - @fjf2002
  - #2269, Allow `limit=0` in the request query to return an empty array - @gautam1168, @laurenceisla
- - #2268, Allow returning XML from single-column queries #2268 - @fjf2002
+ - #2268, Allow returning XML from single-column queries - @fjf2002
+ - #2300, RPC POST for function w/single unnamed XML param #2300 - @fjf2002
 
 ### Fixed
 
diff --git a/src/PostgREST/DbStructure.hs b/src/PostgREST/DbStructure.hs
index e1a1949f2..33e3b2098 100644
--- a/src/PostgREST/DbStructure.hs
+++ b/src/PostgREST/DbStructure.hs
@@ -263,7 +263,7 @@ procsSqlQuery pgVer = [q|
       ) ORDER BY idx) AS args,
       CASE COUNT(*) - COUNT(name) -- number of unnamed arguments
         WHEN 0 THEN true
-        WHEN 1 THEN (array_agg(type))[1] IN ('bytea'::regtype, 'json'::regtype, 'jsonb'::regtype, 'text'::regtype)
+        WHEN 1 THEN (array_agg(type))[1] IN ('bytea'::regtype, 'json'::regtype, 'jsonb'::regtype, 'text'::regtype, 'xml'::regtype)
         ELSE false
       END AS callable
     FROM pg_proc,
diff --git a/src/PostgREST/Error.hs b/src/PostgREST/Error.hs
index 12f73b6f1..00b9c5d47 100644
--- a/src/PostgREST/Error.hs
+++ b/src/PostgREST/Error.hs
@@ -148,6 +148,7 @@ instance JSON.ToJSON ApiRequestError where
       (case (hasPreferSingleObject, isInvPost, contentType) of
         (True, _, _)                 -> " function with a single json or jsonb parameter"
         (_, True, CTTextPlain)       -> " function with a single unnamed text parameter"
+        (_, True, CTTextXML)         -> " function with a single unnamed xml parameter"
         (_, True, CTOctetStream)     -> " function with a single unnamed bytea parameter"
         (_, True, CTApplicationJSON) -> prms <> " function or the " <> schema <> "." <> procName <>" function with a single unnamed json or jsonb parameter"
         _                            -> prms <> " function") <>
diff --git a/src/PostgREST/Request/ApiRequest.hs b/src/PostgREST/Request/ApiRequest.hs
index 85422a1fd..ef82ba25e 100644
--- a/src/PostgREST/Request/ApiRequest.hs
+++ b/src/PostgREST/Request/ApiRequest.hs
@@ -255,6 +255,7 @@ apiRequest conf@AppConfig{..} dbStructure req reqBody queryparams@QueryParams{..
       let paramsMap = M.fromList $ (T.decodeUtf8 *** JSON.String . T.decodeUtf8) <$> parseSimpleQuery (LBS.toStrict reqBody) in
       Right $ ProcessedJSON (JSON.encode paramsMap) $ S.fromList (M.keys paramsMap)
     (CTTextPlain, True) -> Right $ RawPay reqBody
+    (CTTextXML, True) -> Right $ RawPay reqBody
     (CTOctetStream, True) -> Right $ RawPay reqBody
     (ct, _) -> Left $ "Content-Type not acceptable: " <> ContentType.toMime ct
   topLevelRange = fromMaybe allRange $ M.lookup "limit" ranges -- if no limit is specified, get all the request rows
@@ -462,6 +463,7 @@ findProc qi argumentsKeys paramsAsSingleObject allProcs contentType isInvPost =
       (CTApplicationJSON, "json")  -> True
       (CTApplicationJSON, "jsonb") -> True
       (CTTextPlain, "text")        -> True
+      (CTTextXML, "xml")           -> True
       (CTOctetStream, "bytea")     -> True
       _                            -> False
     hasSingleUnnamedParam _ = False
@@ -475,7 +477,7 @@ findProc qi argumentsKeys paramsAsSingleObject allProcs contentType isInvPost =
         then length params == 1 && (firstType == Just "json" || firstType == Just "jsonb")
       -- If the function has no parameters, the arguments keys must be empty as well
       else if null params
-        then null argumentsKeys && not (isInvPost && contentType `elem` [CTTextPlain, CTOctetStream])
+        then null argumentsKeys && not (isInvPost && contentType `elem` [CTOctetStream, CTTextPlain, CTTextXML])
       -- A function has optional and required parameters. Optional parameters have a default value and
       -- don't require arguments for the function to be executed, required parameters must have an argument present.
       else case L.partition ppReq params of
diff --git a/test/spec/Feature/Query/RpcSpec.hs b/test/spec/Feature/Query/RpcSpec.hs
index 85bce16ae..36d0ce21f 100644
--- a/test/spec/Feature/Query/RpcSpec.hs
+++ b/test/spec/Feature/Query/RpcSpec.hs
@@ -1202,6 +1202,13 @@ spec actualPgVersion =
             `shouldRespondWith`
             [str|unnamed text arg|]
 
+        it "can insert xml directly" $
+          request methodPost "/rpc/unnamed_xml_param"
+            [("Content-Type", "text/xml"), ("Accept", "text/xml")]
+            [str|<note><from>John</from><to>Jane</to><message>Remember me</message></note>|]
+            `shouldRespondWith`
+            [str|<note><from>John</from><to>Jane</to><message>Remember me</message></note>|]
+
         it "can insert bytea directly" $ do
           let file = unsafePerformIO $ BL.readFile "test/spec/fixtures/image.png"
           r <- request methodPost "/rpc/unnamed_bytea_param"
@@ -1240,6 +1247,21 @@ spec actualPgVersion =
               , matchHeaders = [ matchContentTypeJson ]
               }
 
+        it "will err when no function with single unnamed text parameter exists and text/xml is specified" $
+          request methodPost "/rpc/unnamed_int_param"
+              [("Content-Type", "text/xml")]
+              [str|a simple text|]
+            `shouldRespondWith`
+              [json|{
+                "hint": "If a new function was created in the database with this name and parameters, try reloading the schema cache.",
+                "message": "Could not find the test.unnamed_int_param function with a single unnamed xml parameter in the schema cache",
+                "code":"PGRST202",
+                "details":null
+              }|]
+              { matchStatus  = 404
+              , matchHeaders = [ matchContentTypeJson ]
+              }
+
         it "will err when no function with single unnamed bytea parameter exists and application/octet-stream is specified" $
           let file = unsafePerformIO $ BL.readFile "test/spec/fixtures/image.png" in
           request methodPost "/rpc/unnamed_int_param"
@@ -1329,3 +1351,18 @@ spec actualPgVersion =
               { matchStatus  = 300
               , matchHeaders = [matchContentTypeJson]
               }
+
+        it "should fail on /rpc/unnamed_xml_param when posting invalid xml" $ do
+          request methodPost "/rpc/unnamed_xml_param"
+            [("Content-Type", "text/xml"), ("Accept", "text/xml")]
+            [str|<|]
+            `shouldRespondWith`
+              [json| {
+                "hint":null,
+                "message":"invalid XML content",
+                "code":"2200N",
+                "details":"line 1: StartTag: invalid element name\n<\n ^"
+              }|]
+              { matchStatus  = 400
+              , matchHeaders = [matchContentTypeJson]
+              }
diff --git a/test/spec/fixtures/schema.sql b/test/spec/fixtures/schema.sql
index dcc334e8b..f616cc034 100644
--- a/test/spec/fixtures/schema.sql
+++ b/test/spec/fixtures/schema.sql
@@ -2312,6 +2312,10 @@ create or replace function test.unnamed_text_param(text) returns text as $$
   select $1;
 $$ language sql;
 
+create or replace function test.unnamed_xml_param(pg_catalog.xml) returns pg_catalog.xml as $$
+  select $1;
+$$ language sql;
+
 create or replace function test.unnamed_bytea_param(bytea) returns bytea as $$
   select $1::bytea;
 $$ language sql;