diff --git a/CHANGELOG.md b/CHANGELOG.md
index 67debfab9..1d798cae1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,10 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  - #3435, Add log-level=debug, for development purposes - @steve-chavez
  - #1526, Add `/metrics` endpoint on admin server - @steve-chavez
    - Exposes connection pool metrics, schema cache metrics
+ - #3404, Show the failed MESSAGE or DETAIL in the `details` field of the `PGRST121` (could not parse RAISE 'PGRST') error - @laurenceisla
+ - #3404, Show extra information in the `PGRST121` (could not parse RAISE 'PGRST') error - @laurenceisla
+   + Shows the failed MESSAGE or DETAIL in the `details` field
+   + Shows the correct JSON format in the `hints` field
 
 ### Fixed
 
@@ -30,10 +34,11 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  - #3330, Incorrect admin server `/ready` response on slow schema cache loads - @steve-chavez
  - #3340, Log when the LISTEN channel gets a notification - @steve-chavez
  - #3345, Fix in-database configuration values not loading for `pgrst.server_trace_header` and `pgrst.server_cors_allowed_origins` - @laurenceisla
- - #3361, Clarify PGRST204(column not found) error message - @steve-chavez
+ - #3361, Clarify the `PGRST204` (column not found) error message - @steve-chavez
  - #3373, Remove rejected mediatype `application/vnd.pgrst.object+json` from response - @taimoorzaeem
  - #3418, Fix OpenAPI not tagging a FK column correctly on O2O relationships - @laurenceisla
  - #3256, Fix wrong http status for pg error `42P17 infinite recursion` - @taimoorzaeem
+ - #3404, Clarify the `PGRST121` (could not parse RAISE 'PGRST') error message - @laurenceisla
 
 ### Deprecated
 
diff --git a/src/PostgREST/ApiRequest/Types.hs b/src/PostgREST/ApiRequest/Types.hs
index b4c075954..e4fb6dc32 100644
--- a/src/PostgREST/ApiRequest/Types.hs
+++ b/src/PostgREST/ApiRequest/Types.hs
@@ -25,6 +25,7 @@ module PostgREST.ApiRequest.Types
   , OrderNulls(..)
   , OrderTerm(..)
   , QPError(..)
+  , RaiseError(..)
   , RangeError(..)
   , SingleVal
   , TrileanVal(..)
@@ -95,12 +96,17 @@ data ApiRequestError
   | OffLimitsChangesError Int64 Integer
   | PutMatchingPkError
   | SingularityError Integer
-  | PGRSTParseError
+  | PGRSTParseError RaiseError
   | MaxAffectedViolationError Integer
   deriving Show
 
 data QPError = QPError Text Text
   deriving Show
+data RaiseError
+  = MsgParseError ByteString
+  | DetParseError ByteString
+  | NoDetail
+  deriving Show
 data RangeError
   = NegativeLimit
   | LowerGTUpper
diff --git a/src/PostgREST/Error.hs b/src/PostgREST/Error.hs
index 31288bf83..eefe57943 100644
--- a/src/PostgREST/Error.hs
+++ b/src/PostgREST/Error.hs
@@ -34,6 +34,7 @@ import Network.HTTP.Types.Header (Header)
 
 import           PostgREST.ApiRequest.Types (ApiRequestError (..),
                                              QPError (..),
+                                             RaiseError (..),
                                              RangeError (..))
 import           PostgREST.MediaType        (MediaType (..))
 import qualified PostgREST.MediaType        as MediaType
@@ -90,7 +91,7 @@ instance PgrstError ApiRequestError where
   status OffLimitsChangesError{}     = HTTP.status400
   status PutMatchingPkError          = HTTP.status400
   status SingularityError{}          = HTTP.status406
-  status PGRSTParseError             = HTTP.status500
+  status PGRSTParseError{}           = HTTP.status500
   status MaxAffectedViolationError{} = HTTP.status400
 
   headers _ = mempty
@@ -187,8 +188,11 @@ instance JSON.ToJSON ApiRequestError where
     (Just "Only is null or not is null filters are allowed on embedded resources")
     Nothing
 
-  toJSON PGRSTParseError = toJsonPgrstError
-    ApiRequestErrorCode21 "The message and detail field of RAISE 'PGRST' error expects JSON" Nothing Nothing
+  toJSON (PGRSTParseError raiseErr) = toJsonPgrstError
+    ApiRequestErrorCode21
+    "Could not parse JSON in the \"RAISE SQLSTATE 'PGRST'\" error"
+    (Just $ JSON.String $ pgrstParseErrorDetails raiseErr)
+    (Just $ JSON.String $ pgrstParseErrorHint raiseErr)
 
   toJSON (InvalidPreferences prefs) = toJsonPgrstError
     ApiRequestErrorCode22
@@ -387,6 +391,17 @@ relHint rels = T.intercalate ", " (hintList <$> rels)
     -- An ambiguousness error cannot happen for computed relationships TODO refactor so this mempty is not needed
     hintList ComputedRelationship{} = mempty
 
+pgrstParseErrorDetails :: RaiseError -> Text
+pgrstParseErrorDetails err = case err of
+  MsgParseError m -> "Invalid JSON value for MESSAGE: '" <> T.decodeUtf8 m <> "'"
+  DetParseError d -> "Invalid JSON value for DETAIL: '" <> T.decodeUtf8 d <> "'"
+  NoDetail        -> "DETAIL is missing in the RAISE statement"
+
+pgrstParseErrorHint :: RaiseError -> Text
+pgrstParseErrorHint err = case err of
+  MsgParseError _ -> "MESSAGE must be a JSON object with obligatory keys: 'code', 'message' and optional keys: 'details', 'hint'."
+  _               -> "DETAIL must be a JSON object with obligatory keys: 'status', 'headers' and optional key: 'status_text'."
+
 data PgError = PgError Authenticated SQL.UsageError
 type Authenticated = Bool
 
@@ -394,9 +409,9 @@ instance PgrstError PgError where
   status (PgError authed usageError) = pgErrorStatus authed usageError
 
   headers (PgError _ (SQL.SessionUsageError (SQL.QueryError _ _ (SQL.ResultError (SQL.ServerError "PGRST" m d _ _p))))) =
-    case (parseMessage m, parseDetails d) of
-      (Just _, Just r) -> headers PGRSTParseError ++ map intoHeader (M.toList $ getHeaders r)
-      _                -> headers PGRSTParseError
+    case parseRaisePGRST m d of
+      Right (_, r) -> map intoHeader (M.toList $ getHeaders r)
+      Left e       -> headers e
     where
       intoHeader (k,v) = (CI.mk $ T.encodeUtf8 k, T.encodeUtf8 v)
 
@@ -426,13 +441,13 @@ instance JSON.ToJSON SQL.QueryError where
 instance JSON.ToJSON SQL.CommandError where
   -- Special error raised with code PGRST, to allow full response control
   toJSON (SQL.ResultError (SQL.ServerError "PGRST" m d _ _p)) =
-    case (parseMessage m, parseDetails d) of
-      (Just r, Just _) -> JSON.object [
+    case parseRaisePGRST m d of
+      Right (r, _) -> JSON.object [
         "code"     .= getCode r,
         "message"  .= getMessage r,
         "details"  .= checkMaybe (getDetails r),
         "hint"     .= checkMaybe (getHint r)]
-      _ -> JSON.toJSON PGRSTParseError
+      Left e      -> JSON.toJSON e
     where
       checkMaybe = maybe JSON.Null JSON.String
 
@@ -493,9 +508,9 @@ pgErrorStatus authed (SQL.SessionUsageError (SQL.QueryError _ _ (SQL.ResultError
         "42501"   -> if authed then HTTP.status403 else HTTP.status401 -- insufficient privilege
         'P':'T':n -> fromMaybe HTTP.status500 (HTTP.mkStatus <$> readMaybe n <*> pure m)
         "PGRST"   ->
-          case (parseMessage m, parseDetails d) of
-            (Just _, Just r) -> maybe (toEnum $ getStatus r) (HTTP.mkStatus (getStatus r) . T.encodeUtf8) (getStatusText r)
-            _                -> status PGRSTParseError
+          case parseRaisePGRST m d of
+            Right (_, r) -> maybe (toEnum $ getStatus r) (HTTP.mkStatus (getStatus r) . T.encodeUtf8) (getStatusText r)
+            Left e       -> status e
         _         -> HTTP.status400
 
     _                       -> HTTP.status500
@@ -579,11 +594,12 @@ instance JSON.FromJSON PgRaiseErrDetails where
 
   parseJSON _ = mzero
 
-parseMessage :: ByteString -> Maybe PgRaiseErrMessage
-parseMessage = JSON.decodeStrict
-
-parseDetails :: Maybe ByteString -> Maybe PgRaiseErrDetails
-parseDetails d = JSON.decodeStrict =<< d
+parseRaisePGRST :: ByteString -> Maybe ByteString -> Either ApiRequestError (PgRaiseErrMessage, PgRaiseErrDetails)
+parseRaisePGRST m d = do
+  msgJson <- maybeToRight (PGRSTParseError $ MsgParseError m) (JSON.decodeStrict m)
+  det <- maybeToRight (PGRSTParseError NoDetail) d
+  detJson <- maybeToRight (PGRSTParseError $ DetParseError det) (JSON.decodeStrict det)
+  return (msgJson, detJson)
 
 -- Error codes are grouped by common modules or characteristics
 data ErrorCode
diff --git a/test/spec/Feature/Query/RpcSpec.hs b/test/spec/Feature/Query/RpcSpec.hs
index 4887e8fac..60ae3d343 100644
--- a/test/spec/Feature/Query/RpcSpec.hs
+++ b/test/spec/Feature/Query/RpcSpec.hs
@@ -1452,17 +1452,29 @@ spec actualPgVersion =
           resHeaders `shouldSatisfy` elem ("X-Header", "str")
           resBody `shouldBe` [json|{"code":"123","message":"ABC","details":null,"hint":null}|]
 
-      it "returns error for invalid JSON in RAISE Message field" $
+      it "returns error for invalid JSON in the MESSAGE option of the RAISE statement" $
         get "/rpc/raise_sqlstate_invalid_json_message" `shouldRespondWith`
-          [json|{"code":"PGRST121","message":"The message and detail field of RAISE 'PGRST' error expects JSON","details":null,"hint":null}|]
+          [json|{
+            "code":"PGRST121",
+            "message":"Could not parse JSON in the \"RAISE SQLSTATE 'PGRST'\" error",
+            "details":"Invalid JSON value for MESSAGE: 'INVALID'",
+            "hint":"MESSAGE must be a JSON object with obligatory keys: 'code', 'message' and optional keys: 'details', 'hint'."}|]
           { matchStatus = 500 }
 
-      it "returns error for invalid JSON in RAISE Details field" $
+      it "returns error for invalid JSON in the DETAIL option of the RAISE statement" $
         get "/rpc/raise_sqlstate_invalid_json_details" `shouldRespondWith`
-          [json|{"code":"PGRST121","message":"The message and detail field of RAISE 'PGRST' error expects JSON","details":null,"hint":null}|]
+          [json|{
+            "code":"PGRST121",
+            "message":"Could not parse JSON in the \"RAISE SQLSTATE 'PGRST'\" error",
+            "details":"Invalid JSON value for DETAIL: 'INVALID'",
+            "hint":"DETAIL must be a JSON object with obligatory keys: 'status', 'headers' and optional key: 'status_text'."}|]
           { matchStatus = 500 }
 
-      it "returns error for missing Details field in RAISE" $
+      it "returns error for missing DETAIL option in the RAISE statement" $
         get "/rpc/raise_sqlstate_missing_details" `shouldRespondWith`
-          [json|{"code":"PGRST121","message":"The message and detail field of RAISE 'PGRST' error expects JSON","details":null,"hint":null}|]
+          [json|{
+            "code":"PGRST121",
+            "message":"Could not parse JSON in the \"RAISE SQLSTATE 'PGRST'\" error",
+            "details":"DETAIL is missing in the RAISE statement",
+            "hint":"DETAIL must be a JSON object with obligatory keys: 'status', 'headers' and optional key: 'status_text'."}|]
           { matchStatus = 500 }